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To distinguish whether the geometry of the coordination center is trigonal bipyramidal or square pyramidal, the (originally just ) parameter was proposed by Addison et al.:
where: are the two greatest valence angles of the coordination center.
When is close to 0 the geometry is similar to square pyramidal, while if is close to 1 the geometry is similar to trigonal bipyramidal: | 1 | Crystallography |
The chromatographic purification of proteins from complex mixtures can be quite challenging, particularly when the mixtures contain similarly retained proteins or when it is desired to enrich trace components in the feed. Further, column loading is often limited when high resolutions are required using traditional modes of chromatography (e.g. linear gradient, isocratic chromatography). In these cases, displacement chromatography is an efficient technique for the purification of proteins from complex mixtures at high column loadings in a variety of applications.
An important advance in the state of the art of displacement chromatography was the development of low molecular mass displacers for protein purification in ion exchange systems. This research was significant in that it represented a major departure from the conventional wisdom that large polyelectrolyte polymers are required to displace proteins in ion exchange systems.
Low molecular mass displacers have significant operational advantages as compared to large polyelectrolyte displacers. For example, if there is any overlap between the displacer and the protein of interest, these low molecular mass materials can be readily separated from the purified protein during post-displacement processing using standard size-based purification methods (e.g. size exclusion chromatography, ultrafiltration). In addition, the salt-dependent adsorption behavior of these low MW displacers greatly facilitates column regeneration. These displacers have been employed for a wide variety of high resolution separations in ion exchange systems. In addition, the utility of displacement chromatography for the purification of recombinant growth factors, antigenic vaccine proteins and antisense oligonucleotides has also been demonstrated. There are several examples in which displacement chromatography has been applied to the purification of proteins using ion exchange, hydrophobic interaction, as well as reversed-phase chromatography.
Displacement chromatography is well suited for obtaining mg quantities of purified proteins from complex mixtures using standard analytical chromatography columns at the bench scale. It is also particularly well suited for enriching trace components in the feed. Displacement chromatography can be readily carried out using a variety of resin systems including, ion exchange, HIC and RPLC. | 0 | Chromatography + Titration + pH indicators |
There are several ways to mathematically define quasicrystalline patterns. One definition, the "cut and project" construction, is based on the work of Harald Bohr (mathematician brother of Niels Bohr). The concept of an almost periodic function (also called a quasiperiodic function) was studied by Bohr, including work of Bohl and Escanglon.
He introduced the notion of a superspace. Bohr showed that quasiperiodic functions arise as restrictions of high-dimensional periodic functions to an irrational slice (an intersection with one or more hyperplanes), and discussed their Fourier point spectrum. These functions are not exactly periodic, but they are arbitrarily close in some sense, as well as being a projection of an exactly periodic function.
In order that the quasicrystal itself be aperiodic, this slice must avoid any lattice plane of the higher-dimensional lattice. De Bruijn showed that Penrose tilings can be viewed as two-dimensional slices of five-dimensional hypercubic structures; similarly, icosahedral quasicrystals in three dimensions are projected from a six-dimensional hypercubic lattice, as first described by Peter Kramer and Roberto Neri in 1984. Equivalently, the Fourier transform of such a quasicrystal is nonzero only at a dense set of points spanned by integer multiples of a finite set of basis vectors, which are the projections of the primitive reciprocal lattice vectors of the higher-dimensional lattice.
Classical theory of crystals reduces crystals to point lattices where each point is the center of mass of one of the identical units of the crystal. The structure of crystals can be analyzed by defining an associated group. Quasicrystals, on the other hand, are composed of more than one type of unit, so, instead of lattices, quasilattices must be used. Instead of groups, groupoids, the mathematical generalization of groups in category theory, is the appropriate tool for studying quasicrystals.
Using mathematics for construction and analysis of quasicrystal structures is a difficult task for most experimentalists. Computer modeling, based on the existing theories of quasicrystals, however, greatly facilitated this task. Advanced programs have been developed allowing one to construct, visualize and analyze quasicrystal structures and their diffraction patterns. The aperiodic nature of quasicrystals can also make theoretical studies of physical properties, such as electronic structure, difficult due to the inapplicability of Bloch's theorem. However, spectra of quasicrystals can still be computed with error control.
Study of quasicrystals may shed light on the most basic notions related to the quantum critical point observed in heavy fermion metals. Experimental measurements on an Au–Al–Yb quasicrystal have revealed a quantum critical point defining the divergence of the magnetic susceptibility as temperature tends to zero. It is suggested that the electronic system of some quasicrystals is located at a quantum critical point without tuning, while quasicrystals exhibit the typical scaling behaviour of their thermodynamic properties and belong to the well-known family of heavy fermion metals. | 1 | Crystallography |
Amorphous silicon (a-Si) is a popular solar cell material owing to its low cost and ease of production. Owing to disordered structure (Urbach tail), its absorption extends to the energies below the band gap resulting in a wide-range spectral response; however, it has a relatively low solar cell efficiency. Protocrystalline Si (pc-Si:H) also has a relatively low absorption near the band gap, owing to its more ordered crystalline structure. Thus, protocrystalline and amorphous silicon can be combined in a tandem solar cell, where the top thin layer of a-Si:H absorbs short-wavelength light whereas the longer wavelengths are absorbed by the underlying protocrystalline silicon layer. | 1 | Crystallography |
For the hexagonal close-packed structure the derivation is similar. Here the unit cell (equivalent to 3 primitive unit cells) is a hexagonal prism containing six atoms (if the particles in the crystal are atoms). Indeed, three are the atoms in the middle layer (inside the prism); in addition, for the top and bottom layers (on the bases of the prism), the central atom is shared with the adjacent cell, and each of the six atoms at the vertices is shared with other six adjacent cells. So the total number of atoms in the cell is 3 + (1/2)×2 + (1/6)×6×2 = 6. Each atom touches other twelve atoms. Now let be the side length of the base of the prism and be its height. The latter is twice the distance between adjacent layers, i. e., twice the height of the regular tetrahedron whose vertices are occupied by (say) the central atom of the lower layer, two adjacent non-central atoms of the same layer, and one atom of the middle layer "resting" on the previous three. Obviously, the edge of this tetrahedron is . If , then its height can be easily calculated to be , and, therefore, . So the volume of the hcp unit cell turns out to be (3/2) , that is 24 .
It is then possible to calculate the APF as follows: | 1 | Crystallography |
Modified (or screened) methyl orange, an indicator consisting of a solution of methyl orange and xylene cyanol, changes from grey-violet to green as the solution becomes more basic. | 0 | Chromatography + Titration + pH indicators |
Reflection high energy electron diffraction - total reflection angle X-ray spectroscopy is a technique for monitoring the chemical composition of crystals. RHEED-TRAXS analyzes X-ray spectral lines emitted from a crystal as a result of electrons from a RHEED gun colliding with the surface.
RHEED-TRAXS is preferential to X-ray microanalysis (XMA)(such as EDS and WDS) because the incidence angle of the electrons on the surface is very small, typically less than 5°. As a result, the electrons do not penetrate deeply into the crystal, meaning the X-ray emission is restricted to the top of the crystal, allowing for real-time, in-situ monitoring of surface stoichiometry.
The experimental setup is fairly simple. Electrons are fired onto a sample causing X-ray emission. These X-rays are then detected using a silicon-lithium Si-Li crystal placed behind beryllium windows, used to maintain vacuum. | 1 | Crystallography |
ScBCSi (x = 0.52, y = 1.42, z = 1.17 and w = 0.02) has a hexagonal crystal structure with space group Pm2 (No. 187) and lattice constants a = b = 1.43055(8) and c = 2.37477(13) nm. Single crystals of this compound were obtained as an intergrowth phase in a float-zoned single crystal of ScBCSi. This phase is not described in the phase diagram of figure 17 because it is a quaternary compound. Its hexagonal structure is rare and has 79 atomic positions in the unit cell: eight partially occupied Sc sites, 62 B sites, two C sites, two Si sites and six B/C sites. Six B sites and one of the two Si sites have partial occupancies. The associated atomic coordinates, site occupancies and isotropic displacement factors are listed in table X.
There are seven structurally independent icosahedra I1–I7 which are formed by B1–B8, B9–B12, B13–B20, B/C21–B24, B/C25–B29, B30–B37 and B/C38–B42 sites, respectively; B43–B46 sites form the B polyhedron and B47–B53 sites construct the B polyhedron. B54–B59 sites form the irregularly shaped B polyhedron in which only 10.7 boron atoms are available because most of sites are too close to each other to be occupied simultaneously. Ten bridging sites C60–B69 interconnect polyhedron units or other bridging sites to form a 3D boron framework structure. One description of the crystal structure uses three pillar-like units that extend along the c-axis that however results in undesired overlaps between those three pillar-like units. An alternative is to define two pillar-like structure units. Figure 29 shows the boron framework structure of ScBCSi viewed along the c-axis, where the pillar-like units P1 and P2 are colored in dark green and light green respectively and are bridged by yellow icosahedra I4 and I7.
These pillar-like units P1 and P2 are shown in figures 30a and b, respectively. P1 consists of icosahedra I1 and I3, an irregularly shaped B polyhedron and other bridge site atoms where two supericosahedra can be seen above and below the B polyhedron. Each supericosahedron is formed by three icosahedra I1 and three icosahedra I3 and is the same as the supericosahedron O(1) shown in figure 24a.The P2 unit consists of icosahedra I2, I5 and I6, B polyhedron and other bridge site atoms. Eight Sc sites with occupancies between 0.49 (Sc8) and 0.98 (Sc1) spread over the boron framework.
As described above, this hexagonal phase originates from a cubic phase, and thus one may expect a similar structural element in these phases. There is an obvious relation between the hexagonal ab-plane and the cubic (111) plane. Figures 31a and b show the hexagonal (001) and the cubic (111) planes, respectively. Both network structures are almost the same that allows intergrowth of the hexagonal phase in the cubic phase. | 1 | Crystallography |
The Collaborative Computational Project Number 4 in Protein Crystallography (CCP4) was set up in 1979 in the United Kingdom to support collaboration between researchers working in software development and assemble a comprehensive collection of software for structural biology. The CCP4 core team is located at the Research Complex at Harwell (RCaH) at Rutherford Appleton Laboratory (RAL) in Didcot, near Oxford, UK.
CCP4 was originally supported by the UK Science and Engineering Research Council (SERC), and is now supported by the Biotechnology and Biological Sciences Research Council (BBSRC). The project is coordinated at CCLRC Daresbury Laboratory. The results of this effort gave rise to the CCP4 program suite, which is now distributed to academic and commercial users worldwide. | 1 | Crystallography |
In addition to yttrium, a wide range of rare-earth elements from Nd to Lu, except for Eu, can form REB compounds. Seybolt discovered the compound YB in 1960 and its structure was solved by Richards and Kasper in 1969. They reported that YB has a face-centered cubic structure with space group Fmc (No. 226) and lattice constant a = 2.3440(6) nm. There are 13 boron sites B1–B13 and one yttrium site. The B1 sites form one icosahedron and the B2–B9 sites make up another icosahedron. These icosahedra arrange in a thirteen-icosahedron unit (B)B which is shown in figure 4a and is called supericosahedron. The icosahedron formed by the B1 site atoms is located at the center of the supericosahedron. The supericosahedron is one of the basic units of the boron framework of YB. There are two types of supericosahedra: one occupies the cubic face centers and another, which is rotated by 90°, is located at the center of the cell and at the cell edges. Thus, there are eight supericosahedra (1248 boron atoms) in the unit cell.
Another structure unit of YB, shown in figure 4b, is B cluster of 80 boron sites formed by the B10 to B13 sites. All those 80 sites are partially occupied and in total contain only about 42 boron atoms. The B cluster is located at the body center of the octant of the unit cell, i.e., at the 8a position (1/4, 1/4, 1/4); thus, there are eight such clusters (336 boron atoms) per unit cell. Two independent structure analyses came to the same conclusion that the total number of boron atoms in the unit cell is 1584. The boron framework structure of YB is shown in figure 5a. To indicate relative orientations of the supericosahedra, a schematic drawing is shown in figure 5b, where the supericosahedra and the B clusters are depicted by light green and dark green spheres, respectively; at the top surface of the unit cell, the relative orientations of the supericosahedra are indicated by arrows. There are 48 yttrium sites ((0.0563, 1/4, 1/4) for YB) in the unit cell. Richards and Kasper fixed the Y site occupancy to 0.5 that resulted in 24 Y atoms in the unit cell and the chemical composition of YB. As shown in figure 6, Y sites form a pair separated by only 0.264 nm in YB. This pair is aligned normal to the plane formed by four supericosahedra. The Y site occupancy 0.5 implies that the pair has always one Y atom with one empty site.
Slack et al. reported that the total number of boron atoms in the unit cell, calculated from the measured values of density, chemical composition and lattice constant, is 1628 ± 4, which is larger than the value 1584 obtained from the structural analysis. The number of B atoms in the unit cell remains nearly constant when the chemical composition changes from YB to YB. On the other hand, the total number of yttrium atoms per unit cell varies, and it is, for example, ~26.3 for YB (see right table). If the total number of Y atoms stays below or equal to 24 then it is possible that one Y atom accommodates in each Y pair (partial occupancy). However, the experimental value of 26.3 significantly exceeds 24, and thus both pair sites might be occupied. In this case, because of the small separation between the two Y atoms, they must be repelled by the Coulomb force. To clarify this point, split Y sites were introduced in the structure analysis resulting in a better agreement with the experiment. The Y site distances and occupancies are presented in the left table.
There are twenty Y pair sites with one Y atom and three pairs with two Y atoms; there is also one empty Y pair (partial occupancy = 0). The separation 0.340 nm for the Y2 pair site (two Y atoms in the pair site) is much larger than the separation 0.254 nm for the Y1 pair site (one Y atom in the pair site), as expected. The total number of Y atoms in the unit cell is 26.3, exactly as measured. Both cases are compared in figure 7. The larger separation for the Y2 pair site is clear as compared with that for the Y1 pair site. In case of the Y2 pair, some neighboring boron sites that belong to the B cluster must be unoccupied because they are too close to the Y2 site.
Splitting the Y site yields right number of Y atoms in the unit cell, but not B atoms. Not only the occupation of the B sites in the B cluster must be strongly dependent on whether or not the Y site is the Y1 state or the Y2 state, but also the position of the occupied B sites must be affected by the state of the Y site. Atomic coordinates and site occupancies are summarized in table II. | 1 | Crystallography |
The most common type of mass spectrometer (MS) associated with a gas chromatograph (GC) is the quadrupole mass spectrometer, sometimes referred to by the Hewlett-Packard (now Agilent) trade name "Mass Selective Detector" (MSD). Another relatively common detector is the ion trap mass spectrometer. Additionally one may find a magnetic sector mass spectrometer, however these particular instruments are expensive and bulky and not typically found in high-throughput service laboratories. Other detectors may be encountered such as time of flight (TOF), tandem quadrupoles (MS-MS) (see below), or in the case of an ion trap MS where n indicates the number mass spectrometry stages. | 0 | Chromatography + Titration + pH indicators |
When dissolved in water, the dye has a blue-violet colour with an absorbance maximum at 590 nm and an extinction coefficient of 87,000 M cm. The colour of the dye depends on the acidity of the solution. At a pH of +1.0, the dye is green with absorption maxima at 420 nm and 620 nm, while in a strongly acidic solution (pH −1.0), the dye is yellow with an absorption maximum at 420 nm.
The different colours are a result of the different charged states of the dye molecule. In the yellow form, all three nitrogen atoms carry a positive charge, of which two are protonated, while the green colour corresponds to a form of the dye with two of the nitrogen atoms positively charged. At neutral pH, both extra protons are lost to the solution, leaving only one of the nitrogen atoms positive charged. The pK for the loss of the two protons are approximately 1.15 and 1.8.
In alkaline solutions, nucleophilic hydroxyl ions attack the electrophilic central carbon to produce the colourless triphenylmethanol or carbinol form of the dye. Some triphenylmethanol is also formed under very acidic conditions when the positive charges on the nitrogen atoms lead to an enhancement of the electrophilic character of the central carbon, which allows the nucleophilic attack by water molecules. This effect produces a slight fading of the yellow colour. | 0 | Chromatography + Titration + pH indicators |
The reciprocal lattice to a BCC lattice is the FCC lattice, with a cube side of .
It can be proven that only the Bravais lattices which have 90 degrees between (cubic, tetragonal, orthorhombic) have primitive translation vectors for the reciprocal lattice, , parallel to their real-space vectors. | 1 | Crystallography |
RHEED users construct Ewalds spheres to find the crystallographic properties of the sample surface. Ewalds spheres show the allowed diffraction conditions for kinematically scattered electrons in a given RHEED setup. The diffraction pattern at the screen relates to the Ewalds sphere geometry, so RHEED users can directly calculate the reciprocal lattice of the sample with a RHEED pattern, the energy of the incident electrons and the distance from the detector to the sample. The user must relate the geometry and spacing of the spots of a perfect pattern to the Ewalds sphere in order to determine the reciprocal lattice of the sample surface.
The Ewalds sphere analysis is similar to that for bulk crystals, however the reciprocal lattice for the sample differs from that for a 3D material due to the surface sensitivity of the RHEED process. The reciprocal lattices of bulk crystals consist of a set of points in 3D space. However, only the first few layers of the material contribute to the diffraction in RHEED, so there are no diffraction conditions in the dimension perpendicular to the sample surface. Due to the lack of a third diffracting condition, the reciprocal lattice of a crystal surface is a series of infinite rods extending perpendicular to the samples surface. These rods originate at the conventional 2D reciprocal lattice points of the sample's surface.
The Ewald's sphere is centered on the sample surface with a radius equal to the magnitude of the wavevector of the incident electrons,
where λ is the electrons' de Broglie wavelength.
Diffraction conditions are satisfied where the rods of reciprocal lattice intersect the Ewalds sphere. Therefore, the magnitude of a vector from the origin of the Ewalds sphere to the intersection of any reciprocal lattice rods is equal in magnitude to that of the incident beam. This is expressed as
Here, k is the wave vector of the elastically diffracted electrons of the order (hl) at any intersection of reciprocal lattice rods with Ewald's sphere
The projections of the two vectors onto the plane of the sample's surface differ by a reciprocal lattice vector G,
Figure 3 shows the construction of the Ewald's sphere and provides examples of the G, k and k vectors.
Many of the reciprocal lattice rods meet the diffraction condition, however the RHEED system is designed such that only the low orders of diffraction are incident on the detector. The RHEED pattern at the detector is a projection only of the k vectors that are within the angular range that contains the detector. The size and position of the detector determine which of the diffracted electrons are within the angular range that reaches the detector, so the geometry of the RHEED pattern can be related back to the geometry of the reciprocal lattice of the sample surface through use of trigonometric relations and the distance from the sample to detector.
The k vectors are labeled such that the vector k00 that forms the smallest angle with the sample surface is called the 0th order beam. The 0th order beam is also known as the specular beam. Each successive intersection of a rod and the sphere further from the sample surface is labeled as a higher order reflection.
Because of the way the center of the Ewald's sphere is positioned, the specular beam forms the same angle with the substrate as the incident electron beam. The specular point has the greatest intensity on a RHEED pattern and is labeled as the (00) point by convention. The other points on the RHEED pattern are indexed according to the reflection order they project.
The radius of the Ewalds sphere is much larger than the spacing between reciprocal lattice rods because the incident beam has a very short wavelength due to its high-energy electrons. Rows of reciprocal lattice rods actually intersect the Ewalds sphere as an approximate plane because identical rows of parallel reciprocal lattice rods sit directly in front and behind the single row shown. Figure 3 shows a cross sectional view of a single row of reciprocal lattice rods filling of the diffraction conditions. The reciprocal lattice rods in Figure 3 show the end on view of these planes, which are perpendicular to the computer screen in the figure.
The intersections of these effective planes with the Ewalds sphere forms circles, called Laue circles. The RHEED pattern is a collection of points on the perimeters of concentric Laue circles around the center point. However, interference effects between the diffracted electrons still yield strong intensities at single points on each Laue circle. Figure 4 shows the intersection of one of these planes with the Ewalds Sphere.
The azimuthal angle affects the geometry and intensity of RHEED patterns. The azimuthal angle is the angle at which the incident electrons intersect the ordered crystal lattice on the surface of the sample. Most RHEED systems are equipped with a sample holder that can rotate the crystal around an axis perpendicular to the sample surface. RHEED users rotate the sample to optimize the intensity profiles of patterns. Users generally index at least 2 RHEED scans at different azimuth angles for reliable characterization of the crystal's surface structure. Figure 5 shows a schematic diagram of an electron beam incident on the sample at different azimuth angles.
Users sometimes rotate the sample around an axis perpendicular to the sampling surface during RHEED experiments to create a RHEED pattern called the azimuthal plot. Rotating the sample changes the intensity of the diffracted beams due to their dependence on the azimuth angle. RHEED specialists characterize film morphologies by measuring the changes in beam intensity and comparing these changes to theoretical calculations, which can effectively model the dependence of the intensity of diffracted beams on the azimuth angle. | 1 | Crystallography |
The APE(X)C, or All Purpose Electronic (X) Computer series was designed by Andrew Donald Booth at Birkbeck College, London in the early 1950s. His work on the APE(X)C series was sponsored by the British Rayon Research Association. Although the naming conventions are slightly unclear, it seems the first model belonged to the BRRA. According to Booth, the X stood for X-company.
One of the series was also known as the APE(X)C or All Purpose Electronic X-Ray Computer and was sited at Birkbeck. | 1 | Crystallography |
Phenolphthalein can be synthesized by condensation of phthalic anhydride with two equivalents of phenol under acidic conditions. It was discovered in 1871 by Adolf von Baeyer.
The reaction can also be catalyzed by a mixture of zinc chloride and thionyl chloride. | 0 | Chromatography + Titration + pH indicators |
Integrating traditional and modern methods is a useful way to process albumin.
There are three main steps that combine Cohn fractionation with chromatography: 1) factors I, II, and III are removed via cold ethanol fractionation, 2) Sepharose fast flow ion exchange and sepharose fast flow chromatography procedures are run, and 3) gel filtration is run. The result is albumin with 9% lower aluminum levels with a processing time that is almost twice as fast.
Although it was hard to make chromatographic processing methods widely adopted, global expansion is a work in progress. Various blood components must be readily available at various medical treatment centers around the world. The Institute of Transfusion Medicine in Skopje, North Macedonia is a plasma fractionation center in the Balkans. Their modernized albumin purification process consists of five steps:
# Starting material is plasma that has been pretreated by centrifugation,
# A round of gel filtration is run,
# ion exchange on DEAE Sepharose is run to bind the albumin to the column,
# Albumin is eluted with a sodium acetate buffer, and
# Final polishing with gel filtration.
The end result is a highly pure and safe batch of albumin that is 100% non-pyrogenic, sterile, and free of active HIV virus. The product purity is greater than 98% and the protein content is about 50 g/L. | 0 | Chromatography + Titration + pH indicators |
Content of anthocyanins in the leaves of colorful plant foods such as purple corn, blueberries, or lingonberries, is about ten times higher than in the edible kernels or fruit.
The color spectrum of grape berry leaves may be analysed to evaluate the amount of anthocyanins. Fruit maturity, quality, and harvest time may be evaluated on the basis of the spectrum analysis. | 0 | Chromatography + Titration + pH indicators |
A tube filled with a glucose phosphate broth is inoculated with a sterile transfer loop. The tube is incubated at for 2–5 days. After incubation, 2.5 ml of the medium are transferred to another tube. Five drops of the pH indicator methyl red is added to this tube. The tube is gently rolled between the palms to disperse the methyl red. | 0 | Chromatography + Titration + pH indicators |
The preferential alignment is a criterion of an orientation of a molecule or atom. The preferential alignment can be related to the formation of the crystal structure of an amorphous structure.
For a polymer material with liquid crystals, the liquid crystals are molecules shaped like rigid rods. Just as logs being floated down a river tend to travel parallel to the direction of the river, liquid crystals have a preferential alignment with each other. At high temperatures, this alignment is disrupted and the material is said to be in the isotropic state. At lower temperatures, the alignment will take place and the liquid crystals are said to be in the pneumatic state [Hoong.C.C]. | 1 | Crystallography |
Denaturing High Performance Liquid Chromatography (DHPLC) is a method of chromatography for the detection of base substitutions, small deletions or insertions in the DNA. Thanks to its speed and high resolution, this method is particularly useful for finding polymorphisms in DNA.
In practice, the analysis begins with a standard PCR in order to amplify the fragment of interest. If the amplified region that exhibits the polymorphism(s) is heterozygous, two kinds of fragments corresponding to the allele and the wild polymorphic allele will be present in the PCR product. This first step is followed by a step of denaturation–renaturation to create hetero- and homoduplexes from the two allele populations in the PCR. To find a homozygous polymorphism, proceed in the same way by premixing a DNA wild population to a population of polymorphic DNA to obtain heteroduplexes after the denaturation–renaturation step.
Heteroduplexes are actually double strands of DNA containing a strand from the wild-type allele and a sprig from the polymorphic allele. The formation of such DNA fragments then causes the appearance of a "mismatch" or bad pairing where the polymorphism is located.
These "mismatches" in the heteroduplex are the basis for the polymorphism detection by DHPLC. Heteroduplexes are thermally less stable than their corresponding homoduplexes, and the single DNA strands will therefore be disconnected by chromatography when subjected to a sufficiently high temperature. The consequence of this double strand instability will be a mismatch of the two DNA strands in the region of polymorphism when DNA is heated to the DNA melting temperature. This mismatch will therefore decrease the interaction with the column and will result in a reduced retention time compared to the homoduplexes in the chromatographic separation process.
To observe the phenomenon of separation, the DHPLC method uses a column of a non-grafted porous stationary phase composed of polystyrene-divinylbenzene alkyl. The stationary phase is electrically neutral and hydrophobic. The DNA, however, is negatively charged at its phosphate groups and therefore can adsorb itself on the column. In order to make the adsorption possible, triethylammonium acetate (TEAA) is used. The positively charged ammonium ion of these molecules interacts with the DNA, and the alkyl chain with the hydrophobic surface of the solid phase.
Therefore, when heteroduplexes are partially denaturated by heating, the negative charges undergo partial relocation and the interaction force between DNA heteroduplexes and column decreases in comparison to the strength of interaction of the homoduplexes. These will therefore be eluted less rapidly by the mobile phase (consisting of acetonitrile). | 0 | Chromatography + Titration + pH indicators |
* Books (chronological order):
** Tanner, Brian: X-ray diffraction topography. Pergamon Press (1976)..
** Authier, André and Lagomarsino, Stefano and Tanner, Brian K. (editors): X-Ray and Neutron Dynamical Diffraction – Theory and Applications. Plenum Press / Kluwer Academic Publishers (1996). .
** Bowen, Keith and Tanner, Brian: High Resolution X-Ray Diffractometry and Topography. Taylor and Francis (1998). .
** Authier, André: Dynamical theory of X-ray diffraction. IUCr monographs on crystallography, no. 11. Oxford University Press (1st edition 2001/ 2nd edition 2003). .
* Reviews
** Lang, A. R.: Techniques and interpretation in X-ray topography. In: Diffraction and Imaging Techniques in Materials Science (edited by Amelinckx S., Gevers R. and Van Landuyt J.) 2nd ed. rev. (1978), pp 623–714. Amsterdam: North Holland.
** Klapper, Helmut: X-ray topography of organic crystals. In: Crystals: Growth, Properties and Applications, vol. 13 (1991), pp 109–162. Berlin-Heidelberg: Springer.
** Lang, A. R.: Topography. In: International Tables for Crystallography, Vol. C (1992), Section 2.7, p. 113. Kluwer, Dordrecht.
** Tuomi, T: Synchrotron X-ray topography of electronic materials. Journal of Synchrotron Radiation (2002) 9, 174-178.
** Baruchel, J. and Härtwig, J. and Pernot-Rejmánková, P.: Present state and perspectives of synchrotron radiation diffraction imaging. Journal of Synchrotron Radiation (2002) 9, 107-114.
* Selected original articles (chronological order):
** X-ray topography
*** T. Tuomi, K. Naukkarinen, E. Laurila, P. Rabe: Rapid high resolution X-ray topography with synchrotron radiation. Acta Polytechnica Scandinavica, Ph. Incl. Nucleonics Series No. 100, (1973), 1-8.
** Special applications:
** Instrumentation and beamlines for topography: | 1 | Crystallography |
ScBC (x = 0.27, y = 1.1, z = 0.2) has an orthorhombic crystal structure with space group Pbam (No. 55) and lattice constants of a = 1.73040(6), b = 1.60738(6) and c = 1.44829(6) nm. This phase is indicated as ScBC (phase IV) in the phase diagram of figure 17. This rare orthorhombic structure has 78 atomic positions in the unit cell: seven partially occupied Sc sites, four C sites, 66 B sites including three partially occupied sites and one B/C mixed-occupancy site. Atomic coordinates, site occupancies and isotropic displacement factors are listed in table IX.
More than 500 atoms are available in the unit cell. In the crystal structure, there are six structurally independent icosahedra I1–I6, which are constructed from B1–B12, B13–B24, B25–B32, B33–B40, B41–B44 and B45–B56 sites, respectively; B57–B62 sites form a B polyhedron. The ScBC crystal structure is layered, as shown in figure 26. This structure has been described in terms of two kinds of boron icosahedron layers, L1 and L2. L1 consists of the icosahedra I3, I4 and I5 and the C65 "dimer", and L2 consists of the icosahedra I2 and I6. I1 is sandwiched by L1 and L2 and the B polyhedron is sandwiched by L2.
An alternative description is based on the same B(B)supericosahedron as in the YB structure. In the YB crystal structure, the supericosahedra form 3-dimensional boron framework as shown in figure 5. In this framework, the neighboring supericosahedra are rotated 90° with respect to each other. On the contrary, in ScBC the supericosahedra form a 2-dimensional network where the 90° rotation relation is broken because of the orthorhombic symmetry. The planar projections of the supericosahedron connection in ScBC and YB are shown in figures 27a and b, respectively. In the YB crystal structure, the neighboring 2-dimensional supericosahedron connections are out-of-phase for the rotational relation of the supericosahedron. This allows 3-dimensional
stacking of the 2-dimensional supericosahedron connection while maintaining the cubic symmetry.
The B boron cluster occupies the large space between four supericosahedra as described in the REB section. On the other hand, the 2-dimensional supericosahedron networks in the ScBC crystal structure stack in-phase along the z-axis. Instead of the B cluster, a pair of the I2 icosahedra fills the open space staying within the supericosahedron network, as shown in figure 28 where the icosahedron I2 is colored in yellow.
All Sc atoms except for Sc3 reside in large spaces between the supericosahedron networks, and the Sc3 atom occupies a void in the network as shown in figure 26. Because of the small size of Sc atom, the occupancies of the Sc1–Sc5 sites exceed 95%, and those of Sc6 and Sc7 sites are approximately 90% and 61%, respectively (see table IX). | 1 | Crystallography |
1. Comprehensive Conversion: The reactor converts all organic compounds to methane, whereas traditional methanizers typically only convert CO and CO2. This comprehensive conversion results in a more uniform response and more sensitive detection for a wider range of organic species.
2. Resilience to Poisoning: The reactor is more resilient to poisoning by compounds containing nitrogen and oxygen compared to traditional methanizers. This means that it can maintain its performance and efficiency even in the presence of potentially interfering compounds.
3. Sharper Peaks: When compared with packed column versions of methanizers, the reactor typically produces sharper peaks. Sharper peaks enhance resolution and can improve the accuracy and reliability of chromatographic analysis.
Overall, these benefits make post-column oxidation-reduction reactors an attractive choice for gas chromatography applications where comprehensive conversion, resistance to poisoning, and peak sharpness are essential. | 0 | Chromatography + Titration + pH indicators |
CrysTBox (Crystallographic Tool Box) is a suite of computer tools designed to accelerate material research based on transmission electron microscope images via highly accurate automated analysis and interactive visualization. Relying on artificial intelligence and computer vision, CrysTBox makes routine crystallographic analyses simpler, faster and more accurate compared to human evaluators. The high level of automation together with sub-pixel precision and interactive visualization makes the quantitative crystallographic analysis accessible even for non-crystallographers allowing for an interdisciplinary research. Simultaneously, experienced material scientists can take advantage of advanced functionalities for comprehensive analyses.
CrysTBox is being developed in the Laboratory of electron microscopy at the Institute of Physics of the Czech Academy of Sciences. For academic purposes, it is available for free. As of 2022, the suite has been deployed at research and educational facilities in more than 90 countries supporting research of ETH Zurich, Lawrence Berkeley National Laboratory, Max Planck Institutes, Chinese Academy of Sciences, Fraunhofer Institutes or Oxford University. | 1 | Crystallography |
In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector, for example) does not necessarily have unit size, or even a particular size at all. Rather, the primitive cell is the closest analogy to a unit vector, since it has a determined size for a given lattice and is the basic building block from which larger cells are constructed.
The concept is used particularly in describing crystal structure in two and three dimensions, though it makes sense in all dimensions. A lattice can be characterized by the geometry of its unit cell, which is a section of the tiling (a parallelogram or parallelepiped) that generates the whole tiling using only translations.
There are two special cases of the unit cell: the primitive cell and the conventional cell. The primitive cell is a unit cell corresponding to a single lattice point, it is the smallest possible unit cell. In some cases, the full symmetry of a crystal structure is not obvious from the primitive cell, in which cases a conventional cell may be used. A conventional cell (which may or may not be primitive) is a unit cell with the full symmetry of the lattice and may include more than one lattice point. The conventional unit cells are parallelotopes in n dimensions. | 1 | Crystallography |
The ratio of activities of a solute, A in an aqueous/organic system will remain constant and independent of the total quantity of A (hence ), so at any given temperature:
Distribution constants are useful as they allow the calculation of the concentration of remaining analyte in the solution, even after a number of solvent extractions have occurred. They also provide guidance in choosing the most efficient way to conduct an extractive separation.
Thus, the concentration of A remaining in an aqueous solution after i extractions with an organic solvent can be found using:
(where [A] is the concentration of A remaining after extracting V millilitres of solution with the original concentration of [A] with i portions of the organic solvent, each with a volume of V). | 0 | Chromatography + Titration + pH indicators |
Crystallographic directions are lines linking nodes (atoms, ions or molecules) of a crystal. Similarly, crystallographic planes are planes linking nodes. Some directions and planes have a higher density of nodes; these dense planes have an influence on the behavior of the crystal:
*optical properties: in condensed matter, light "jumps" from one atom to the other with the Rayleigh scattering; the velocity of light thus varies according to the directions, whether the atoms are close or far; this gives the birefringence
*adsorption and reactivity: adsorption and chemical reactions can occur at atoms or molecules on crystal surfaces, these phenomena are thus sensitive to the density of nodes;
*surface tension: the condensation of a material means that the atoms, ions or molecules are more stable if they are surrounded by other similar species; the surface tension of an interface thus varies according to the density on the surface
** Pores and crystallites tend to have straight grain boundaries following dense planes
**cleavage
*dislocations (plastic deformation)
**the dislocation core tends to spread on dense planes (the elastic perturbation is "diluted"); this reduces the friction (Peierls–Nabarro force), the sliding occurs more frequently on dense planes;
**the perturbation carried by the dislocation (Burgers vector) is along a dense direction: the shift of one node in a dense direction is a lesser distortion;
**the dislocation line tends to follow a dense direction, the dislocation line is often a straight line, a dislocation loop is often a polygon.
For all these reasons, it is important to determine the planes and thus to have a notation system. | 1 | Crystallography |
Phenolphthalein ( ) is a chemical compound with the formula CHO and is often written as "HIn", "HPh", "phph" or simply "Ph" in shorthand notation. Phenolphthalein is often used as an indicator in acid–base titrations. For this application, it turns colorless in acidic solutions and pink in basic solutions. It belongs to the class of dyes known as phthalein dyes.
Phenolphthalein is slightly soluble in water and usually is dissolved in alcohols in experiments. It is a weak acid, which can lose H ions in solution. The nonionized phenolphthalein molecule is colorless and the double deprotonated phenolphthalein ion is fuchsia. Further proton loss in higher pH occurs slowly and leads to a colorless form. Phenolphthalein ion in concentrated sulfuric acid is orange red due to sulfonation. | 0 | Chromatography + Titration + pH indicators |
* Orbifold signature:
* Coxeter notation (rectangular): [((∞,2),(∞,2))]
* Coxeter notation (square): [4,4]
* Lattice: rectangular
* Point group: D
* The group pgg contains two rotation centres of order two (180°), and glide reflections in two perpendicular directions. The centres of rotation are not located on the glide reflection axes. There are no reflections.
;Examples of group pgg | 1 | Crystallography |
Usually when describing a space geometrically, a coordinate system is used which consists of a choice of origin and a basis of linearly independent, non-coplanar basis vectors , where is the dimension of the space being described. With reference to this coordinate system, each point in the space can be specified by coordinates (a coordinate -tuple). The origin has coordinates and an arbitrary point has coordinates . The position vector is then,
In -dimensions, the lengths of the basis vectors are denoted and the angles between them . However, most cases in crystallography involve two- or three-dimensional space in which the basis vectors are commonly displayed as with their lengths and angles denoted by and respectively. | 1 | Crystallography |
Though the many advances of HPLC and monoliths are highly visible within the confines of the analytical and pharmaceutical industries, it is unlikely that general society is aware of these developments. Currently, consumers may witness technology developments in the analytical sciences industry in the form of a broader array of available pharmaceutical products of higher purity, advanced forensic testing in criminal trials, better environmental monitoring, and faster returns on medical tests. In the future, presumably, this may not be the case. As medicine becomes more individualized over time, consumer awareness that something is improving their quality of care seems more likely. The further thought that monoliths or HPLC are involved is unlikely to concern the general public, however.
There are two main cost drivers behind technological change in this industry. Though many different analytical areas use LC, including food and beverage industries, forensics labs, and clinical testing facilities, the largest impetus toward technology developments comes from the research and development and production arms of the pharmaceutical industry. The areas in which high-throughput monolithic column technologies are likely to have the largest economic impact are R&D and downstream processing.
From the Research and Development field comes the desire for more resolved, faster separations from smaller sample quantities. The only phase of drug development under direct control of a pharmaceutical company is the R&D stage. The goal of analytical work is to obtain as much information as possible from the sample. At this stage, high-throughput and analysis of tiny sample quantities are critical. Pharmaceutical companies are looking for tools that will better enable them to measure and predict the efficacy of candidate drugs in shorter times and with less expensive clinical trials. To this end, nano-scale separations, highly automated HPLC equipment, and multi-dimensional chromatography have become influential.
The prevailing method to increase the sensitivity of analytical methods has been multi-dimensional chromatography. This practice uses other analysis techniques in conjunction with liquid chromatography. For example, mass spectrometry (MS) has very much gained in popularity as an on-line analytical technique following HPLC. It is limited, however, in that MS, like nuclear magnetic resonance spectroscopy (NMR) or electrospray ionization techniques (ESI), is only feasible when using very small quantities of solute and solvent; LC-MS is used with nano or capillary scale techniques, but cannot be used in prep-scale. Another tactic for increasing selectivity in multi-dimensional chromatography is to use two columns with different selectivity orthogonally; ie... linking an ion exchange column to a C18 endcapped column. In 2007, Karger reported that, through multi-dimensional chromatography and other techniques, starting with only about 12,000 cells containing 1-4μg of protein, he was able to identify 1867 unique proteins. Of those, Karger can isolate 4 that may be of interest as cervical cancer markers. Today, liquid chromatographers using multi-dimensional LC can isolate compounds at the femtomole (10 mole) and attomole (10 mole) levels.
After a drug has been approved by the U.S. Food and Drug Administration (FDA), the emphasis at a pharmaceutical company is on getting a product to market. This is where prep or process scale chromatography has a role. In contrast to analytical analysis, preparatory scale chromatography focuses on isolation and purity of compounds. There is a trade-off between the degree of purity of compound and the amount of time required to achieve that purity. Unfortunately, many of the preparatory or process scale solutions used by pharmaceutical companies are proprietary, due to difficulties in patenting a process. Hence, there is not a great deal of literature available. However, some attempts to address the problems of prep scale chromatography include monoliths and simulated moving beds.
A comparison of immunoglobulin protein capture on a conventional column and a monolithic column yields some economically interesting results. If processing times are equivalent, process volumes of IgG, an antibody, are 3,120L for conventional columns versus 5,538L for monolithic columns. This represents a 78% increase in process volume efficiency, while at the same time only a tenth of the media waste volume is generated. Not only is the monolith column more economically prudent when considering the value of product processing times, but, at the same time, less media is used, representing a significant reduction in variable costs. | 0 | Chromatography + Titration + pH indicators |
The set of databases includes data from International Tables of Crystallography, Vol. A: Space-Group Symmetry, and the data of maximal subgroups of space groups as listed in International Tables of Crystallography, Vol. A1: Symmetry relations between space groups. A k-vector database with Brillouin zone figures and classification tables of the k-vectors for space groups is also available via the [http://www.cryst.ehu.es/cryst/get_kvec.html KVEC] tool. | 1 | Crystallography |
The eluent or eluant is the "carrier" portion of the mobile phase. It moves the analytes through the chromatograph. In liquid chromatography, the eluent is the liquid solvent; in gas chromatography, it is the carrier gas. | 0 | Chromatography + Titration + pH indicators |
APCI generally suffers less ion suppression than ESI, as discussed previously. Where possible, if ion suppression is unavoidable it may be advisable to switch from ESI to APCI. If this is not possible, it may be useful to switch the ESI ionisation mode from positive to negative. Since fewer compounds are ionisable in negative ionisation mode, it is entirely possible that the ion suppressing species may be removed from the analysis. However, it should also be considered that the analyte of interest may not be ionised effectively in negative mode either, rendering this approach useless. | 0 | Chromatography + Titration + pH indicators |
The operating principle of CCC equipment requires a column consisting of a tube coiled around a bobbin. The bobbin is rotated in a double-axis gyratory motion (a cardioid), which causes a variable g-force to act on the column during each rotation. This motion causes the column to see one partitioning step per revolution and components of the sample separate in the column due to their partitioning coefficient between the two immiscible liquid phases. "High-performance" countercurrent chromatography (HPCCC) works in much the same way as HSCCC. A seven-year research and development process produced HPCCC instruments that generated 240 gs, compared to the 80 gs of the HSCCC machines. This increase in g-force and larger bore of the column has enabled a ten-fold increase in throughput, due to improved mobile phase flow rates and a higher stationary phase retention. Countercurrent chromatography is a preparative liquid chromatography technique, however with the advent of the higher-g HPCCC instruments it is now possible to operate instruments with sample loadings as low as a few milligrams, whereas in the past hundreds of milligrams had been necessary. Major application areas for this technique include natural product purification and drug development. | 0 | Chromatography + Titration + pH indicators |
Anionic and cationic surfactants can be determined thermometrically by titrating one type against the other. For instance, benzalkonium chloride (a quaternary-type cationic surfactant) may be determined in cleaners and algaecides for swimming pools and spas by titrating with a standard solution of sodium dodecyl sulfate. Alternatively, anionic surfactants such as sodium lauryl sulfate can be titrated with cetyl pyridinium chloride. | 0 | Chromatography + Titration + pH indicators |
HPTLC finds extensive application in various fields, including pharmaceutical industries, clinical chemistry, forensic chemistry, biochemistry, cosmetology, food and drug analysis, environmental analysis, and more, owing to its numerous advantages. It distinguishes itself by being the only chromatographic method capable of presenting results as images and offers simplicity, cost-effectiveness, parallel analysis of samples, high sample capacity, rapid results, and the option for multiple detection methods.
Le Roux's research team assessed HPTLC for determining salbutamol serum levels in clinical trials and concluded that it is a suitable method for analyzing serum samples.
HPTLC has also been used successfully in the separation of various lipid subclasses, with reproducible and promising results obtained for 20 different lipid subclasses. Numerous reports related to clinical medicine studies have been published in various journals. As a result, HPTLC is now strongly recommended for drug analysis in serum and other tissues. | 0 | Chromatography + Titration + pH indicators |
An SADP is acquired under parallel electron illumination. In the case of convergent beam, a convergent beam electron diffraction (CBED) is achieved. The beam used in SAD is broad illuminating a wide sample area. In order to analyze only a specific sample area, the selected area aperture in the image plane is used. This is in contrast with nanodiffraction, where the site-selectivity is achieved using a beam condensed to a narrow probe. SAD is important in direct imaging for instance when orienting the sample for high resolution microscopy or setting up dark-field imaging conditions.
High-resolution electron microscope images can be transformed into an artificial diffraction pattern using Fourier transform. Then, they can be processed the same way as real diffractograms allowing to determine crystal orientation, measure interplanar angles and distances even with picometric precision.
SAD is similar to X-ray diffraction, but unique in that areas as small as several hundred nanometers in size can be examined, whereas X-ray diffraction typically samples areas much larger. | 1 | Crystallography |
The van Deemter equation relates height equivalent to a theoretical plate (HETP) of a chromatographic column to the various flow and kinetic parameters which cause peak broadening, as follows:
Where
* HETP = a measure of the resolving power of the column [m]
* A = Eddy-diffusion parameter, related to channeling through a non-ideal packing [m]
* B = diffusion coefficient of the eluting particles in the longitudinal direction, resulting in dispersion [m s]
* C = Resistance to mass transfer coefficient of the analyte between mobile and stationary phase [s]
* u = speed [m s]
In open tubular capillaries, the A term will be zero as the lack of packing means channeling does not occur. In packed columns, however, multiple distinct routes ("channels") exist through the column packing, which results in band spreading. In the latter case, A will not be zero.
The form of the Van Deemter equation is such that HETP achieves a minimum value at a particular flow velocity. At this flow rate, the resolving power of the column is maximized, although in practice, the elution time is likely to be impractical. Differentiating the van Deemter equation with respect to velocity, setting the resulting expression equal to zero, and solving for the optimum velocity yields the following: | 0 | Chromatography + Titration + pH indicators |
For calculating concentrations, an ICE table can be used. ICE stands for initial, change, and equilibrium.
The pH of a weak acid solution being titrated with a strong base solution can be found at different points along the way. These points fall into one of four categories:
# initial pH
# pH before the equivalence point
# pH at the equivalence point
# pH after the equivalence point
1. The initial pH is approximated for a weak acid solution in water using the equation:
where is the initial concentration of the hydronium ion.
2. The pH before the equivalence point depends on the amount of weak acid remaining and the amount of conjugate base formed. The pH can be calculated approximately by the Henderson–Hasselbalch equation: where K is the acid dissociation constant.
3. The pH at the equivalence point depends on how much the weak acid is consumed to be converted into its conjugate base. Note that when an acid neutralizes a base, the pH may or may not be neutral (pH = 7). The pH depends on the strengths of the acid and base. In the case of a weak acid and strong base titration, the pH is greater than 7 at the equivalence point. Thus pH can be calculated using the following formula:
Where is the concentration of the hydroxide ion. The concentration of the hydroxide ion is calculated from the concentration of the hydronium ion and using the following relationship:
Where K is the base dissociation constant, K is the water dissociation constant.
4. The pH after the equivalence point depends on the concentration of the conjugate base of the weak acid and the strong base of the titrant. However, the base of the titrant is stronger than the conjugate base of the acid. Therefore, the pH in this region is controlled by the strong base. As such the pH can be found using the following:
where is the concentration of the strong base that is added, is the volume of base added until the equilibrium, is the concentration of the strong acid that is added, and is the initial volume of the acid. | 0 | Chromatography + Titration + pH indicators |
Standard column chromatography consists of a solid stationary phase and a liquid mobile phase, while gas chromatography (GC) uses a solid or liquid stationary phase on a solid support and a gaseous mobile phase. By contrast, in liquid-liquid chromatography, both the mobile and stationary phases are liquid. The contrast is, however, not as stark as it first appears. In reversed-phase chromatography, for example, the stationary phase can be regarded as a liquid which is immobilized by chemical bonding to a micro-porous silica solid support. In countercurrent chromatography centripetal or gravitational forces immobilize the stationary liquid layer. By eliminating solid supports, permanent adsorption of the analyte onto the column is avoided, and a high recovery of the analyte can be achieved. The countercurrent chromatography instrument is easily switched between normal phase chromatography and reversed-phase chromatography simply by changing the mobile and stationary phases. With column chromatography, the separation potential is limited by the commercially available stationary phase media and its particular characteristics. Nearly any pair of immiscible solutions can be used in countercurrent chromatography provided that the stationary phase can be successfully retained.
Solvent costs are also generally lower than for HPLC. In comparison to column chromatography, flows and total solvent usage can in most countercurrent chromatography separations may be reduced by half and even up to a tenth. Also, the cost of purchasing and disposing of stationary phase media is eliminated. Another advantage of countercurrent chromatography is that experiments conducted in the laboratory can be scaled to industrial volumes. When gas chromatography or HPLC is carried out with large volumes, resolution is lost due to issues with surface-to-volume ratios and flow dynamics; this is avoided when both phases are liquid.
The CCC separation process can be thought of as occurring in three stages: mixing, settling, and separation of the two phases (although they often occur continuously). Vigorous mixing of the phases is critical in order to maximize the interfacial area between them and enhance mass transfer. The analyte will distribute between the phases according to its partition coefficient which is also called the distribution coefficient, distribution constant, or partition ratio and is represented by P, K, D, K, or K. The partition coefficient for an analyte in a particular biphasic solvent system is independent of the volume of the instrument, flow rate, stationary phase retention volume ratio and the g-force required to immobilize the stationary phase. The degree of stationary phase retention is a crucial parameter. Common factors that influence stationary phase retention are flow rate, solvent composition of the biphasic solvent system, and the g-force. The stationary phase retention is represented by the stationary phase volume retention ratio (Sf) which is the volume of the stationary phase divided by the total volume of the instrument. The settling time is a property of the solvent system and the sample matrix, both of which greatly influence stationary phase retention.
To most process chemists, the term "countercurrent" implies two immiscible liquids moving in opposing directions, as typically occurs in large centrifugal extractor units. With the exception of dual flow (see below) CCC, most countercurrent chromatography modes of operation have a stationary phase and a mobile phase. Even in this situation, countercurrent flows occur within the instrument column. Several researchers have proposed renaming both CCC & CPC to liquid-liquid chromatography, but others feel the term "countercurrent" itself is a misnomer.
Unlike column chromatography and HPLC, countercurrent chromatography operators can inject large volumes relative to column volume. Typically 5 to 10% of coil volume can be injected. In some cases this can be increased to as high as 15 to 20% of the coil volume. Typically, most modern commercial CCC and CPC can inject 5 to 40 g/L capacity. The range is so large, even for a specific instrument, let alone all instrument options, as the type of target, matrix and available biphasic solvent vary so much. Approximately 10 g/L would be a more typical value, that the majority of applications could use as a base value.
The countercurrent separation starts with choosing an appropriate biphasic solvent system for the desired separation. A wide array of biphasic solvent mixtures are available to the CCC practitioner including the combination n-hexane (or heptane), ethyl acetate, methanol and water in different proportions. This basic solvent system is sometimes referred to as the HEMWat solvent system. The choice of solvent system may be guided by perusal of the CCC literature. The familiar technique of thin layer chromatography may also be employed to determine an optimal solvent system. The organization of solvent systems into "families" has greatly facilitated the choice of solvent systems as well. A solvent system can be tested with a one-flask partitioning experiment. The measured partition coefficient from the partitioning experiment will indicate the elution behavior of the compound. Typically, it is desirable to choose a solvent system where the target compound(s) have a partition coefficient between 0.25 and 8. Historically, it was thought that no commercial countercurrent chromatograph could cope with the high viscosities of ionic liquids. However, modern instruments that can accommodate 30 to 70+ % ionic liquids (and potentially 100% ionic liquid, if both phases are suitably customized ionic liquids) have become available. Ionic liquids can be customized for polar / non-polar organic, achiral and chiral compounds, bio-molecule, and inorganic separations, as ionic liquids can be customized to have extraordinary solvency and specificity.
After the biphasic solvent system has been chosen a batch of is formulated and equilibrated in a separatory funnel. This step is called pre-equilibration of the solvent system. The two phases are separated. Then the column is filled with stationary with a pump. Next, the column is set an equilibration conditions, such as the desired rotation speed, and the mobile phase is pumped through the column. The mobile phase displaces the a portion of the stationary phase until column equilibration is achieved and the mobile phase elutes from the column. The sample may be introduced into the column at any time during the column equilibration step or after equilibration has been accomplished. After the volume of eluant surpasses the volume of the mobile phase in the column, the sample components will begin to elute. Compounds with a partition coefficient of unity will elute when one column volume of mobile phase has passed through the column since the time of injection. The compound can then be introduced to another stationary phase to help increase the resolution of results. The flow is stopped after the target compound(s) are eluted or the column is extruded by pumping the stationary phase through the column. An example of a major application of countercurrent chromatography is to take an extremely complex matrix such as a plant extract, perform the countercurrent chromatography separation with a carefully selected solvent system, and extrude the column to recover all of the sample. The original complex matrix will have been fractionated into discrete narrow polarity bands, which may then be assayed for chemical composition or bioactivity. Performing one or more countercurrent chromatography separations in conjunction with other chromatographic and non chromatographic techniques has the potential for rapid advances in compositional recognition of extremely complex matrices. | 0 | Chromatography + Titration + pH indicators |
It may cause irritation. Its toxicological properties have not been fully investigated. Harmful if swallowed, Acute Toxicity. Only Hazardous when percent values are above 10%. | 0 | Chromatography + Titration + pH indicators |
Cubic materials are special orthotropic materials that are invariant with respect to 90° rotations with respect to the principal axes, i.e., the material is the same along its principal axes. Due to these additional symmetries the stiffness tensor can be written with just three different material properties like
The inverse of this matrix is commonly written as
where is the Youngs modulus, is the shear modulus, and is the Poissons ratio. Therefore, we can think of the ratio as the relation between the shear modulus for the cubic material and its (isotropic) equivalent: | 1 | Crystallography |
The Wigner–Seitz cell, named after Eugene Wigner and Frederick Seitz, is a primitive cell which has been constructed by applying Voronoi decomposition to a crystal lattice. It is used in the study of crystalline materials in crystallography.
The unique property of a crystal is that its atoms are arranged in a regular three-dimensional array called a lattice. All the properties attributed to crystalline materials stem from this highly ordered structure. Such a structure exhibits discrete translational symmetry. In order to model and study such a periodic system, one needs a mathematical "handle" to describe the symmetry and hence draw conclusions about the material properties consequent to this symmetry. The Wigner–Seitz cell is a means to achieve this.
A Wigner–Seitz cell is an example of a primitive cell, which is a unit cell containing exactly one lattice point. For any given lattice, there are an infinite number of possible primitive cells. However there is only one Wigner–Seitz cell for any given lattice. It is the locus of points in space that are closer to that lattice point than to any of the other lattice points.
A Wigner–Seitz cell, like any primitive cell, is a fundamental domain for the discrete translation symmetry of the lattice. The primitive cell of the reciprocal lattice in momentum space is called the Brillouin zone. | 1 | Crystallography |
Bravais lattices, also referred to as space lattices, describe the geometric arrangement of the lattice points, and therefore the translational symmetry of the crystal. The three dimensions of space afford 14 distinct Bravais lattices describing the translational symmetry. All crystalline materials recognized today, not including quasicrystals, fit in one of these arrangements. The fourteen three-dimensional lattices, classified by lattice system, are shown above.
The crystal structure consists of the same group of atoms, the basis, positioned around each and every lattice point. This group of atoms therefore repeats indefinitely in three dimensions according to the arrangement of one of the Bravais lattices. The characteristic rotation and mirror symmetries of the unit cell is described by its crystallographic point group. | 1 | Crystallography |
The basic working principle of diffraction topography is as follows:
An incident, spatially extended beam (mostly of X-rays, or neutrons) impinges on a sample.
The beam may be either monochromatic, i.e. consist one single wavelength of X-rays or neutrons, or polychromatic, i.e. be composed of a mixture of wavelengths ("white beam" topography). Furthermore, the incident beam may be either parallel, consisting only of "rays" propagating all along nearly the same direction, or divergent/convergent, containing several more strongly different directions of propagation.
When the beam hits the crystalline sample, Bragg diffraction occurs, i.e. the incident wave is reflected by the atoms on certain lattice planes of the sample, if it hits those planes at the right Bragg angle.
Diffraction from sample can take place either in reflection geometry (Bragg case), with the beam entering and leaving through the same surface, or in transmission geometry (Laue case).
Diffraction gives rise to a diffracted beam, which will leave the sample and propagate along a direction differing from the incident direction by the scattering angle .
The cross section of the diffracted beam may or may not be identical to the one of the incident beam. In the case of strongly asymmetric reflections, the beam size (in the diffraction plane) is considerably expanded or compressed, with expansion occurring if the incidence angle is much smaller than the exit angle, and vice versa. Independently of this beam expansion, the relation of sample size to image size is given by the exit angle alone: The apparent lateral size of sample features parallel to the exit surface is downscaled in the image by the projection effect of the exit angle.
A homogeneous sample (with a regular crystal lattice) would yield a homogeneous intensity distribution in the topograph (a "flat" image with no contrast). Intensity modulations (topographic contrast) arise from irregularities in the crystal lattice, originating from various kinds of defects such as
* voids and inclusions in the crystal
* phase boundaries (regions of different crystallographic phase, polytype, ...)
* defective areas, non-crystalline (amorphous) areas / inclusions
* cracks, surface scratches
* stacking faults
* dislocations, dislocation bundles
* grain boundaries, domain walls
* growth striations
* point defects or defect clusters
* crystal deformation
* strain fields
In many cases of defects such as dislocations, topography is not directly sensitive to the defects themselves (atomic structure of the dislocation core), but predominantly to the strain field surrounding the defect region. | 1 | Crystallography |
There have been a few technical issues that have limited adoption of SFC technology in the past. First of all, is the need to keep a high gas pressure in the operating conditions. High-pressure vessels are expensive and bulky, and special materials are often needed to avoid dissolving gaskets and O-rings in the supercritical fluid. A second drawback is difficulty in maintaining pressure constant (by back-pressure regulation). Whereas liquids are nearly incompressible, so their densities are constant regardless of pressure, supercritical fluids are highly compressible and their physical properties change with pressure – such as the pressure drop across a packed-bed column. Currently, automated backpressure regulators can maintain a constant pressure in the column even if flow rate varies, mitigating this problem. A third drawback is difficulty in gas/liquid separation during collection of product. Upon depressurization, the CO rapidly turns into gas and aerosolizes any dissolved analyte in the process. Cyclone separators have lessened difficulties in gas/liquid separations. | 0 | Chromatography + Titration + pH indicators |
The injection valve is a motorized valve which links the mixer and sample loop to the column. Typically the valve has three positions for loading the sample loop, for injecting the sample from the loop into the column, and for connecting the pumps directly to the waste line to wash them or change buffer solutions. The injection valve has a sample loading port through which the sample can be loaded into the injection loop, usually from a hypodermic syringe using a Luer-lock connection. | 0 | Chromatography + Titration + pH indicators |
Gadolinium is given to patients for magnetic resonance imaging, or an MRI.It is used as a contrast agent for the exam to improve clarity of the images formed. However, it can react in the human body and have detrimental effects. Therefore, the agent should be removed. One of these gadolinium based agents is gadodiamide. Calcium in the body should be determined accurately to ensure that the Gadodiamide does not have adverse effects on the patient. There are two o-cresolphthalein methods to determine amount of calcium. The o-cresolpthalein methods are effective because it is a calcium binding dye. The gadolinium ion with a charge of +3 can be removed from gadodiamide using o-cresolphthalein. For these methods, glomerular filtration rate, or GFR, and time since gadodiamide was given should be recorded. Ultimately, these two factors and the impact of gadodiamide on calcium levels calculated by the o-cresolphthalein method helps to reveal an amount of time that patients must wait after receiving gadodiamide to have blood drawn again, or avoid pseudohypocalcemia. | 0 | Chromatography + Titration + pH indicators |
There are many types of titrations with different procedures and goals. The most common types of qualitative titration are acid–base titrations and redox titrations. | 0 | Chromatography + Titration + pH indicators |
In solid-state physics and crystallography, a crystal structure is described by a unit cell repeating periodically over space. There are an infinite number of choices for unit cells, with different shapes and sizes, which can describe the same crystal, and different choices can be useful for different purposes.
Say that a crystal structure is described by a unit cell U. Another unit cell S is a supercell of unit cell U, if S is a cell which describes the same crystal, but has a larger volume than cell U. Many methods which use a supercell perturbate it somehow to determine properties which cannot be determined by the initial cell. For example, during phonon calculations by the small displacement method, phonon frequencies in crystals are calculated using force values on slightly displaced atoms in the supercell. Another very important example of a supercell is the conventional cell of body-centered (bcc) or face-centered (fcc) cubic crystals. | 1 | Crystallography |
A common problem to X-ray crystallography and electron crystallography is radiation damage, by which especially organic molecules and proteins are damaged as they are being imaged, limiting the resolution that can be obtained. This is especially troublesome in the setting of electron crystallography, where that radiation damage is focused on far fewer atoms. One technique used to limit radiation damage is electron cryomicroscopy, in which the samples undergo cryofixation and imaging takes place at liquid nitrogen or even liquid helium temperatures. Because of this problem, X-ray crystallography has been much more successful in determining the structure of proteins that are especially vulnerable to radiation damage. Radiation damage was recently investigated using MicroED of thin 3D crystals in a frozen hydrated state. | 1 | Crystallography |
TLC helps show the purity of a sample. A pure sample should only contain one spot by TLC. TLC is also useful for small-scale purification. Because the separated compounds will be on different areas of the plate, a scientist can scrape off the stationary phase particles containing the desired compound and dissolve them into an appropriate solvent. Once all the compound dissolves in the solvent, they filter out the silica particles, then evaporate the solvent to isolate the product. Big preparative TLC plates with thick silica gel coatings can separate more than 100 mg of material.
For larger-scale purification and isolation, TLC is useful to quickly test solvent mixtures before running flash column chromatography on a large batch of impure material. A compound elutes from a column when the amount of solvent collected is equal to 1/R. The eluent from flash column chromatography gets collected across several containers (for example, test tubes) called fractions. TLC helps show which fractions contain impurities and which contain pure compound.
Furthermore, two-dimensional TLC can help check if a compound is stable on a particular stationary phase. This test requires two runs on a square-shaped TLC plate. The plate is rotated by 90º before the second run. If the target compound appears on the diagonal of the square, it is stable on the chosen stationary phase. Otherwise, it is decomposing on the plate. If this is the case, an alternative stationary phase may prevent this decomposition.
TLC is also an analytical method for the direct separation of enantiomers and the control of enantiomeric purity, e.g. active pharmaceutical ingredients (APIs) that are chiral. | 0 | Chromatography + Titration + pH indicators |
The APPI interface for LC–MS was developed simultaneously by Bruins and Syage in 2000. APPI is another LC–MS ion source/ interface for the analysis of neutral compounds that cannot be ionized using ESI. This interface is similar to the APCI ion source, but instead of a corona discharge, the ionization occurs by using photons coming from a discharge lamp. In the direct-APPI mode, singly charged analyte molecular ions are formed by absorption of a photon and ejection of an electron. In the dopant-APPI mode, an easily ionizable compound (Dopant) is added to the mobile phase or the nebulizing gas to promote a reaction of charge-exchange between the dopant molecular ion and the analyte. The ionized sample is later transferred to the mass analyzer at high vacuum as it passes through small orifice skimmers. | 0 | Chromatography + Titration + pH indicators |
It can be shown that there are four types of Euclidean plane isometries. (Note: the notations for the types of isometries listed below are not completely standardised.) | 1 | Crystallography |
The Pearson symbol should only be used to designate simple structures (elements, some binary compound) where the number of atoms per unit cell equals, ideally, the number of translationally equivalent points. | 1 | Crystallography |
*Significant improvement of resolution in data collection
*Reduced or eliminated radiation damage in crystals | 1 | Crystallography |
Multiple isomorphous replacement (MIR), where heavy atoms are inserted into structure (usually by synthesizing proteins with analogs or by soaking) | 1 | Crystallography |
The development of the APCI interface for LC–MS started with Horning and collaborators in the early 1973. However, its commercial application was introduced at the beginning of the 1990s after Henion and collaborators improved the LC–APCI–MS interface in 1986. The APCI ion source/ interface can be used to analyze small, neutral, relatively non-polar, and thermally stable molecules (e.g., steroids, lipids, and fat soluble vitamins). These compounds are not well ionized using ESI. In addition, APCI can also handle mobile phase streams containing buffering agents. The liquid from the LC system is pumped through a capillary and there is also nebulization at the tip, where a corona discharge takes place. First, the ionizing gas surrounding the interface and the mobile phase solvent are subject to chemical ionization at the ion source. Later, these ions react with the analyte and transfer their charge. The sample ions then pass through small orifice skimmers by means of or ion-focusing lenses. Once inside the high vacuum region, the ions are subject to mass analysis. This interface can be operated in positive and negative charge modes and singly-charged ions are mainly produced. APCI ion source can also handle flow rates between 500 and 2000 μl/min and it can be directly connected to conventional 4.6 mm ID columns. | 0 | Chromatography + Titration + pH indicators |
Butter yellow was synthesized by Peter Griess in the 1860s at the Royal College of Chemistry in London. The dye was used to dye butter in Germany and other parts of the world during the latter half of the 19th century and the beginning of the 20th before being phased out in the 1930s and 40s. It was in the 1930s that research led by Riojun Kinosita showed the link between several azo dyes and cancer, linking butter yellow to liver cancer in rats after two to three months exposure. In 1939, the International Congress for Cancer Research issued a recommendation for the banning of cancer-causing food dyes (including butter yellow) from food production.
In 2014, dried tofu products (a.k.a. dougan 豆乾) from Taiwan were found to have been adulterated with methyl yellow, used as a coloring agent. | 0 | Chromatography + Titration + pH indicators |
SFC has been used primarily for separation of chiral molecules, mainly those which required normal phase conditions. While the mobile phase is a fluid in the supercritical state, the stationary phase is packed inside columns similar to those used in liquid chromatography. Since the use of normal phase mode of chromatography remained less common, so did SFC; therefore it is now commonly used for selected chiral and achiral separations and purification in the pharmaceutical industry. | 0 | Chromatography + Titration + pH indicators |
Of the 32 crystallographic point groups, 10 are polar:
The space groups associated with a polar point group do not have a discrete set of possible origin points that are unambiguously determined by symmetry elements.
When materials having a polar point group crystal structure are heated or cooled, they may temporarily generate a voltage called pyroelectricity.
Molecular crystals which have symmetry described by one of the polar space groups, such as sucrose, may exhibit triboluminescence. | 1 | Crystallography |
There are two types of pumps available for uniform delivery of relatively small liquid volumes for GPC: piston or peristaltic pumps. The delivery of a constant flow free of fluctuations is especially important to the precision of the GPC analysis, as the flow-rate is used for the calibration of the molecular weight, or diameter. | 0 | Chromatography + Titration + pH indicators |
In addition to the operations of the point group, the space group of the crystal structure contains translational symmetry operations. These include:
*Pure translations, which move a point along a vector
*Screw axes, which rotate a point around an axis while translating parallel to the axis.
*Glide planes, which reflect a point through a plane while translating it parallel to the plane.
There are 230 distinct space groups. | 1 | Crystallography |
After crystallization, often some solidified flux remains on the surface or inside the desired crystal. This flux may cause defects in the crystal due to the different thermal expansivities of the flux and crystal. A solvent (typically an acid or a base) can dissolve the flux, but its difficult to find a solvent that doesnt also dissolve the crystal. The flux can be removed mechanically using a blade or drill. If the crystal and flux have significantly different boiling points, the flux may be removed with evaporation. Flux can also be removed through recrystallization through use of a seed in the liquid phase, leaving the flux behind as the crystals accumulate.
The removal of excess flux is important to assess a crystals properties, as the flux can affect measurements. For example, tin and lead super conduct at low temperatures, if a sample has tin or lead flux superconductivity can be observed even if the desired crystal is not a superconductor. | 1 | Crystallography |
Cleavage forms parallel to crystallographic planes:
*Basal, pinacoidal, or planar cleavage occurs when there is only cleavage plane. Talc has basal cleavage. Mica (like muscovite or biotite) also has basal cleavage; this is why mica can be peeled into thin sheets.
*Prismatic cleavage occurs when there are cleavage planes in a crystal that intersect at 90 degrees. Spodumene exhibits prismatic cleavage.
*Non-Prismatic cleavage occurs when there are cleavage planes in a crystal that do not intersect at 90 degrees (two non-perpendicular directions of cleavage, e.g 60 & 120 degrees).
*Cubic cleavage occurs when there are cleavage planes intersecting at 90 degrees. Halite (or salt) has cubic cleavage, and therefore, when halite crystals are broken, they will form more cubes.
*Rhombohedral cleavage occurs when there are cleavage planes intersecting at angles that are not 90 degrees. Calcite has rhombohedral cleavage.
*Octahedral cleavage occurs when there are cleavage planes in a crystal. Fluorite exhibits perfect octahedral cleavage. Octahedral cleavage is common for semiconductors. Diamond also has octahedral cleavage.
*Dodecahedral cleavage occurs when there are cleavage planes in a crystal. Sphalerite has dodecahedral cleavage. | 1 | Crystallography |
Capillary electrophoresis (CE) is a family of electrokinetic separation methods performed in submillimeter diameter capillaries and in micro- and nanofluidic channels. Very often, CE refers to capillary zone electrophoresis (CZE), but other electrophoretic techniques including capillary gel electrophoresis (CGE), capillary isoelectric focusing (CIEF), capillary isotachophoresis and micellar electrokinetic chromatography (MEKC) belong also to this class of methods. In CE methods, analytes migrate through electrolyte solutions under the influence of an electric field. Analytes can be separated according to ionic mobility and/or partitioning into an alternate phase via non-covalent interactions. Additionally, analytes may be concentrated or "focused" by means of gradients in conductivity and pH. | 0 | Chromatography + Titration + pH indicators |
The Knudsen effusion cell was developed by Martin Knudsen (1871–1949). A typical Knudsen cell contains a crucible (made of pyrolytic boron nitride, quartz, tungsten or graphite), heating filaments (often made of metal tantalum), water cooling system, heat shields, and an orifice shutter. | 1 | Crystallography |
Malachite green is an organic compound that is used as a dyestuff and controversially as an antimicrobial in aquaculture. Malachite green is traditionally used as a dye for materials such as silk, leather, and paper. Despite its name the dye is not prepared from the mineral malachite; the name just comes from the similarity of color. | 0 | Chromatography + Titration + pH indicators |
In the Euclidean plane, we have the following possibilities.
*; [ ] Identity
:Two reflections in the same mirror restore each point to its original position. All points are left fixed. Any pair of identical mirrors has the same effect.
*; [] Reflection
:As Alice found through the looking-glass, a single mirror causes left and right hands to switch. (In formal terms, topological orientation is reversed.) Points on the mirror are left fixed. Each mirror has a unique effect.
*; [] Rotation
:Two distinct intersecting mirrors have a single point in common, which remains fixed. All other points rotate around it by twice the angle between the mirrors. Any two mirrors with the same fixed point and same angle give the same rotation, so long as they are used in the correct order.
*; [] Translation
:Two distinct mirrors that do not intersect must be parallel. Every point moves the same amount, twice the distance between the mirrors, and in the same direction. No points are left fixed. Any two mirrors with the same parallel direction and the same distance apart give the same translation, so long as they are used in the correct order.
*; [] Glide reflection
:Three mirrors. If they are all parallel, the effect is the same as a single mirror (slide a pair to cancel the third). Otherwise we can find an equivalent arrangement where two are parallel and the third is perpendicular to them. The effect is a reflection combined with a translation parallel to the mirror. No points are left fixed. | 1 | Crystallography |
Perovskites can be deposited as epitaxial thin films on top of other perovskites, using techniques such as pulsed laser deposition and molecular-beam epitaxy. These films can be a couple of nanometres thick or as small as a single unit cell. The well-defined and unique structures at the interfaces between the film and substrate can be used for interface engineering, where new types properties can arise. This can happen through several mechanisms, from mismatch strain between the substrate and film, change in the oxygen octahedral rotation, compositional changes, and quantum confinement. An example of this is LaAlO grown on SrTiO, where the interface can exhibit conductivity, even though both LaAlO and SrTiO are non-conductive. Another example is SrTiO grown on LSAT ((LaAlO) (SrAlTaO)) or DyScO can morph the incipient ferroelectric into a ferroelectric at room temperature through the means of epitaxially applied biaxial strain. The lattice mismatch of GdScO to SrTiO (+1.0%) applies tensile stress resulting in a decrease of the out-of-plane lattice constant of SrTiO, compared to LSAT (−0.9 %), which epitaxially applies compressive stress leading to an extension of the out-of-plane lattice constant of SrTiO (and subsequent increase of the in-plane lattice constant). | 1 | Crystallography |
The APE(X)C series included the following machines:
* APE(X)C: Birkbeck College, London, first time operated in May 1952, ready for use at the end of 1953
* APE(N)C: Board of Mathematical Machines, Oslo (N likely stands for Norway), also known as NUSSE
* APE(H)C: British Tabulating Machine Company (It is unclear what H stands for - perhaps Hollerith as the company sold Hollerith Unit record equipment
* APE(R)C: British Rayon Research Association (R stands for Rayon), ready for use in June 1952
* UCC: University College, London (circa January 1956)
* MAC or MAGIC (Magnetic Automatic Calculator): "built by Wharf Engineering Laboratories" (February 1955)
* The HEC (Hollerith Electronic Computer), built by the British Tabulating Machine Company (later to become International Computers and Tabulators (ICT), then International Computers Limited (ICL)), a commercial machine sold in several models and later known as the ICT200 series. There were likely the derivatives HEC 1, HEC 2, HEC 2M - M for marketable denoting the machine's orientation toward commercial rather than scientific customers, and HEC 4 (before 1955)
Only one of each of these machines was built, with the exception of HEC (and possibly MAC) which were commercial machines produced in quite large numbers for the time, around 150. They were similar in design, with various small differences, mostly in I/O equipment. The APEHC was a punched card machine while the APEXC, APERC and APENC were teletypers (keyboard and printer, plus paper tape reader and puncher). Also, the UCC had 8k words of storage, instead of 1k word for other machines, and the MAC used germanium diodes in replacement of many valves. | 1 | Crystallography |
Quantum crystallography is a branch of crystallography that investigates crystalline materials within the framework of quantum mechanics, with analysis and representation, in position or in momentum space, of quantities like wave function, electron charge and spin density, density matrices and all properties related to them (like electric potential, electric or magnetic moments, energy densities, electron localization function, one electron potential, etc.).
Like the quantum chemistry, Quantum crystallography involves both experimental and computational work. The theoretical part of quantum crystallography is based on quantum mechanical calculations of atomic/molecular/crystal wave functions, density matrices or density models, used to simulate the electronic structure of a crystalline material. While in quantum chemistry, the experimental works mainly rely on spectroscopy, in quantum crystallography the scattering techniques (X-rays, neutrons, γ-Rays, electrons) play the central role, although spectroscopy as well as atomic microscopy are also sources of information.
The connection between crystallography and quantum chemistry has always been very tight, after X-ray diffraction techniques became available in crystallography. In fact, the scattering of radiation enables mapping the one-electron distribution or the elements of a density matrix.
The kind of radiation and scattering determines the quantity which is represented (electron charge or spin) and the space in which it is represented (position or momentum space).
Although the wave function is typically assumed not to be directly measurable, recent advances enable also to compute wave functions that are restrained to some experimentally measurable observable (like the scattering of a radiation).
The term Quantum Crystallography was first introduced in revisitation articles by L. Huang, L. Massa and Nobel Prize winner Jerome Karle, who associated it with two mainstreams: a) crystallographic information that enhances quantum mechanical calculations and b) quantum mechanical approaches to improve crystallography information. This definition mainly refers to studies started in the 1960s and 1970s, when first attempts to obtain wave functions from scattering experiments appeared, together with other methods to constrain a wavefunction to experimental observations like the dipole moment. This field has been recently reviewed, within the context of this definition.
Parallel to studies on wave function determination, R. F. Stewart and P. Coppens investigated the possibilities to compute models for one-electron charge density from X-ray scattering (for example by means of pseudoatoms multipolar expansion), and later of spin density from polarized neutron diffraction, that originated the scientific community of charge, spin and momentum density.
In a recent review article, V. Tsirelson gave a more general definition: "Quantum crystallography is a research area exploiting the fact that parameters of quantum-mechanically valid electronic model of a crystal can be derived from the accurately measured set of X-ray coherent diffraction structure factors".
The book Modern Charge Density Analysis offers a survey of the research involving Quantum Crystallography and of the most adopted experimental or theoretical methodologies.
The International Union of Crystallography has recently established a commission on Quantum Crystallography, as extension of the previous commission on Charge, Spin and Momentum density, with the purpose of coordinating research activities in this field. | 1 | Crystallography |
Convergent beam electron diffraction (CBED) is an electron diffraction technique where a convergent or divergent beam (conical electron beam) of electrons is used to study materials. | 1 | Crystallography |
The relationship between fractional and Cartesian coordinates can be described by the matrix transformation :
Similarly, the Cartesian coordinates can be converted back to fractional coordinates using the transformation : | 1 | Crystallography |
Mixed-mode chromatography (MMC), or multimodal chromatography, refers to chromatographic methods that utilize more than one form of interaction between the stationary phase and analytes in order to achieve their separation. What is distinct from conventional single-mode chromatography is that the secondary interactions in MMC cannot be too weak, and thus they also contribute to the retention of the solutes. | 0 | Chromatography + Titration + pH indicators |
"Euhedral" is derived from the Greek eu meaning "well, good" and hedron meaning a seat or a face of a solid. | 1 | Crystallography |
For an infinite three-dimensional lattice , defined by its primitive vectors and the subscript of integers , its reciprocal lattice with the integer subscript can be determined by generating its three reciprocal primitive vectors
where is the scalar triple product. The choice of these is to satisfy as the known condition (There may be other condition.) of primitive translation vectors for the reciprocal lattice derived in the heuristic approach above and the section multi-dimensional Fourier series. This choice also satisfies the requirement of the reciprocal lattice mathematically derived above. Using column vector representation of (reciprocal) primitive vectors, the formulae above can be rewritten using matrix inversion:
This method appeals to the definition, and allows generalization to arbitrary dimensions. The cross product formula dominates introductory materials on crystallography.
The above definition is called the "physics" definition, as the factor of comes naturally from the study of periodic structures. An essentially equivalent definition, the "crystallographer's" definition, comes from defining the reciprocal lattice . which changes the reciprocal primitive vectors to be
and so on for the other primitive vectors. The crystallographer's definition has the advantage that the definition of is just the reciprocal magnitude of in the direction of , dropping the factor of . This can simplify certain mathematical manipulations, and expresses reciprocal lattice dimensions in units of spatial frequency. It is a matter of taste which definition of the lattice is used, as long as the two are not mixed.
is conventionally written as or , called Miller indices; is replaced with , replaced with , and replaced with . Each lattice point in the reciprocal lattice corresponds to a set of lattice planes in the real space lattice. (A lattice plane is a plane crossing lattice points.) The direction of the reciprocal lattice vector corresponds to the normal to the real space planes. The magnitude of the reciprocal lattice vector is given in reciprocal length and is equal to the reciprocal of the interplanar spacing of the real space planes. | 1 | Crystallography |
The intense coloring of the molecule is generated by the absorption of specific wavelengths of light by the pi bonds. These bonds are ordinarily excited by light in the orange region of the spectrum, causing the molecule to appear blue. When the molecule interacts with protons from an acid the bonds become harder to excite and thus absorb green light which has a shorter wavelength. This is what causes the molecule to appear red in the presence of an acid. | 0 | Chromatography + Titration + pH indicators |
The use of electronic detectors such as X-ray CCD cameras, replacing traditional X-ray film, facilitates topography in many ways. CCDs achieve online readout in (almost) real-time, dispensing experimentalists of the need to develop films in a dark room. Drawbacks with respect to films are the limited dynamic range and, above all, the moderate spatial resolution of commercial CCD cameras, making the development of dedicated CCD cameras necessary for high-resolution imaging. A further, decisive advantage of digital topography is the possibility to record series of images without changing detector position, thanks to online readout. This makes it possible, without complicated image registration procedures, to observe time-dependent phenomena, to perform kinetic studies, to investigate processes of device degradation and radiation damage, and to realize sequential topography (see below). | 1 | Crystallography |
For a one-dimensional crystal of size
where the factor in parentheses comes from the fact the sum is over nearest-neighbour pairs (), next nearest-neighbours (), ... and for a crystal of planes, there are pairs of nearest neighbours, pairs of next-nearest neighbours, etc. | 1 | Crystallography |
After the molecules travel the length of the column, pass through the transfer line and enter into the mass spectrometer they are ionized by various methods with typically only one method being used at any given time. Once the sample is fragmented it will then be detected, usually by an electron multiplier, which essentially turns the ionized mass fragment into an electrical signal that is then detected.
The ionization technique chosen is independent of using full scan or SIM. | 0 | Chromatography + Titration + pH indicators |
Centrifugal partition chromatography has been extensively used for isolation and purification of natural products for 40 years. Due to the ability to get very high selectivity, and the ability to tolerate samples containing particulated matter, it is possible to work with direct extracts of biomass, opposed to traditional liquid chromatography, where impurities degrade the solid stationary phase so that separation become impossible.
There are numerous laboratory scale centrifugal partition chromatography manufacturers around the world, like Gilson (Armen Instrument), Kromaton (Rousselet Robatel), and AECS-QUIKPREP. These instruments operate at flow rates of 1–500 mL/min. with stationary phase retentions of 40–80%. | 0 | Chromatography + Titration + pH indicators |
Two-dimensional liquid chromatography (2D-LC) combines two separate analyses of liquid chromatography into one data analysis. Modern 2D liquid chromatography has its origins in the late 1970s to early 1980s. During this time, the hypothesized principles of 2D-LC were being proven via experiments conducted along with supplementary conceptual and theoretical work. It was shown that 2D-LC could offer quite a bit more resolving power compared to the conventional techniques of one-dimensional liquid chromatography. In the 1990s, the technique of 2D-LC played an important role in the separation of extremely complex substances and materials found in the proteomics and polymer fields of study. Unfortunately, the technique had been shown to have a significant disadvantage when it came to analysis time. Early work with 2D-LC was limited to small portion of liquid phase separations due to the long analysis time of the machinery. Modern 2D-LC techniques tackled that disadvantage head on, and have significantly reduced what was once a damaging feature. Modern 2D-LC has an instrumental capacity for high resolution separations to be completed in an hour or less. Due to the growing need for instrumentation to perform analysis on substances of growing complexity with better detection limits, the development of 2D-LC pushes forward. Instrumental parts have become a mainstream industry focus and are much easier to attain then before. Prior to this, 2D-LC was performed using components from 1D-LC instruments, and would lead to results of varying degrees in both accuracy and precision. The reduced stress on instrumental engineering has allowed for pioneering work in the field and technique of 2D-LC.
The purpose of employing this technique is to separate mixtures that one-dimensional liquid chromatography otherwise cannot separate effectively. Two-dimensional liquid chromatography is better suited to analyzing complex mixtures samples such as urine, environmental substances and forensic evidence such as blood.
Difficulties in separating mixtures can be attributed to the complexity of the mixture in the sense that separation cannot occur due to the number of different effluents in the compound. Another problem associated with one-dimensional liquid chromatography involves the difficulty associated to resolving closely related compounds. Closely related compounds have similar chemical properties that may prove difficult to separate based on polarity, charge, etc. Two-dimensional liquid chromatography provides separation based on more than one chemical or physical property. Using an example from Nagy and Vekey, a mixture of peptides can be separated based on their basicity, but similar peptides may not elute well. Using a subsequent LC technique, the similar basicity between the peptides can be further separated by employing differences in apolar character.
As a result, to be able to separate mixtures more efficiently, a subsequent LC analysis must employ very different separation selectivity relative to the first column. Another requirement to effectively use 2D liquid chromatography, according to Bushey and Jorgenson, is to employ highly orthogonal techniques which means that the two separation techniques must be as different as possible.
There are two major classifications of 2D liquid chromatography. These include: Comprehensive 2D liquid chromatography (LCxLC) and Heart-cutting 2D liquid chromatography (LC-LC). In comprehensive 2D-LC, all the peaks from a column elution are fully sampled, but it has been deemed unnecessary to transfer the entire sample from the first to the second column. A portion of the sample is sent to waste while the rest is sent to the sampling valve. In heart-cutting 2D-LC specific peaks are targeted with only a small portion of the peak being injected onto a second column. Heart-cutting 2D-LC has proven to be quite useful for sample analysis of substances that are not very complex provided they have similar retention behavior. Compared to comprehensive 2D-LC, heart-cutting 2D-LC provides an effective technique with much less system setup and a much lower operating cost. Multiple heart-cutting (mLC-LC) may be utilized to sample multiple peaks from first dimensional analysis without risking temporary overlap of second dimensional analysis. Multiple heart-cutting (mLC-LC) utilizes a setup of multiple sampling loops.
For 2D-LC, peak capacity is a very important issue. This can be generated using gradient elution separation with much greater efficiency than an isocratic separation given a reasonable amount of time. While isocratic elution is much easier on a fast time scale, it is preferable to perform a gradient elution separation in the second dimension. The mobile phase strength is varied from a weak eluent composition to a stronger one. Based on linear solvent strength theory (LSST) of gradient elution for reversed phase chromatography, the relationship between retention time, instrumental variables and solute parameters is shown below.
:t=t +t + t/b*ln(b*(k-t/t) + 1)
While a lot of pioneering work has been completed in the years since 2D-LC became a major analytical chromatographic technique, there are still many modern problems to be considered. Large amounts of experimental variables have yet to be decided on, and the technique is constantly in a state of development. | 0 | Chromatography + Titration + pH indicators |
SAD analysis is widely used in material research for its relative simplicity and high information value. Once the sample is prepared and examined in a modern transmission electron microscope, the device allows for a routine diffraction acquisition in a matter of seconds. If the images are interpreted correctly, they can be used to identify crystal structures, determine their orientations, measure crystal characteristics, examine crystal defects or material textures. The course of analysis depends on whether the diffractogram depicts ring or spot diffraction pattern and on the quantity to be determined.
Software tools based on computer vision algorithms simplifies quantitative analysis. | 1 | Crystallography |
Liquid chromatography as we know it today really got its start in 1969, when the first modern HPLC was designed and marketed as a nucleic acid analyzer. Columns throughout the 1970s were unreliable, pump flow rates were inconsistent, and many biologically active compounds escaped detection by UV and fluorescence detectors. Focus on purification methods in the 70s morphed into faster analyses in the 1980s, when computerized controls were integrated into HPLC equipment. Higher degrees of computerization then led to emphasis on more precise, faster, automated equipment in the 1990s. Atypical of many technologies of the 60s and '70s, the emphasis in improvements was not on “bigger and better,” but on “smaller and better”. At the same time the HPLC user-interface was improving, it was critical to be able to isolate hundreds of peptides or biomarkers from ever decreasing sample sizes.
Laboratory analytical instrumentation has only been recognized as a separate and distinct industry by NAICS and SIC since 1987. This market segmentation includes not only gas and liquid chromatography, but also mass spectrometry and spectrophotometric instruments. Since first recognized as a separate market, sales of analytical laboratory equipment increased from about $3.5 billion in 1987 to more than $26 billion in 2004. Revenues in the world liquid chromatography market, specifically, are expected to grow from $3.4 billion in 2007 to $4.7 billion in 2013, with a slight decrease in spending expected in 2008 and 2009 from the worldwide economic slump and decreased or stagnant spending. The pharmaceutical industry alone accounts for 35% of all the HPLC instruments in use. The main source of growth in LC stems from biosciences and pharmaceutical companies. | 0 | Chromatography + Titration + pH indicators |
The origin of the stereographic projection is not known, but it is believed to have been discovered by Ancient Greek astronomers and used for projecting the celestial sphere to the plane so that the motions of stars and planets could be analyzed using plane geometry. Its earliest extant description is found in Ptolemys Planisphere (2nd century AD), but it was ambiguously attributed to Hipparchus (2nd century BC) by Synesius (), and Apolloniuss Conics () contains a theorem which is crucial in proving the property that the stereographic projection maps circles to circles. Hipparchus, Apollonius, Archimedes, and even Eudoxus (4th century BC) have sometimes been speculatively credited with inventing or knowing of the stereographic projection, but some experts consider these attributions unjustified. Ptolemy refers to the use of the stereographic projection in a "horoscopic instrument", perhaps the described by Vitruvius (1st century BC).
By the time of Theon of Alexandria (4th century), the planisphere had been combined with a dioptra to form the planispheric astrolabe ("star taker"), a capable portable device which could be used for measuring star positions and performing a wide variety of astronomical calculations. The astrolabe was in continuous use by Byzantine astronomers, and was significantly further developed by medieval Islamic astronomers. It was transmitted to Western Europe during the 11th–12th century, with Arabic texts translated into Latin.
In the 16th and 17th century, the equatorial aspect of the stereographic projection was commonly used for maps of the Eastern and Western Hemispheres. It is believed that already the map created in 1507 by Gualterius Lud was in stereographic projection, as were later the maps of Jean Roze (1542), Rumold Mercator (1595), and many others. In star charts, even this equatorial aspect had been utilised already by the ancient astronomers like Ptolemy.
François dAguilon gave the stereographic projection its current name in his 1613 work Opticorum libri sex philosophis juxta ac mathematicis utiles' (Six Books of Optics, useful for philosophers and mathematicians alike).
In the late 16th century, Thomas Harriot proved that the stereographic projection is conformal; however, this proof was never published and sat among his papers in a box for more than three centuries. In 1695, Edmond Halley, motivated by his interest in star charts, was the first to publish a proof. He used the recently established tools of calculus, invented by his friend Isaac Newton. | 1 | Crystallography |
* In acids: violet
* At equivalence point (pH 5.2): grey
* In bases: green
Methylene blue functions to change the red-yellow shift of methyl red to a more distinct violet-green shift. | 0 | Chromatography + Titration + pH indicators |
Of the hundreds of facet arrangements that have been used, the most famous is probably the round brilliant cut, used for diamond and many colored gemstones. This first early version of what would become the modern Brilliant Cut is said to have been devised by an Italian named Peruzzi, sometime in the late 17th century. Later on, the first angles for an "ideal" cut diamond were calculated by Marcel Tolkowsky in 1919. Slight modifications have been made since then, but angles for "ideal" cut diamonds are still similar to Tolkowskys formula. Round brilliants cut before the advent of "ideal" angles are often referred to as "Early round brilliant cut" or "Old European brilliant cut" and are considered poorly cut by todays standards, though there is still interest in them from collectors. Other historic diamond cuts include the "Old Mine Cut" which is similar to early versions of the round brilliant, but has a rectangular outline, and the "Rose Cut" which is a simple cut consisting of a flat, polished back, and varying numbers of angled facets on the crown, producing a faceted dome. Sometimes a 58th facet, called a culet is cut on the bottom of the stone to help prevent chipping of the pavilion point. Earlier brilliant cuts often have very large culets, while modern brilliant cut diamonds generally lack the culet facet, or it may be present in minute size. | 1 | Crystallography |
A wallpaper remains on the whole unchanged under certain isometries, starting with certain translations that confer on the wallpaper a repetitive nature. One of the reasons to be unchanged under certain translations is that it covers the whole plane. No mathematical object in our minds is stuck onto a motionless wall! On the contrary an observer or his eye is motionless in front of a transformation, which glides or rotates or flips a wallpaper, eventually could distort it, but that would be out of our subject.
If an isometry leaves unchanged a given wallpaper, then the inverse isometry keeps it also unchanged, like translation on image 1, 3 or 4, or a ± 120° rotation around a point like S on image 3 or 4. If they have both this property to leave unchanged a wallpaper, two isometries composed in one or the other order have then this same property to leave unchanged the wallpaper. To be exhaustive about the concepts of group and subgroups under the function composition, represented by the circle shaped symbol ⵔ, here is a traditional truism in mathematics: everything remains itself under the identity transformation. This identity function can be called translation of zero vector or rotation of 360°.
A glide can be represented by one or several arrows if parallel and of same length and same sense, in same way a wallpaper can be represented either by a few patterns or by only one pattern, considered as a pseudo‑tile imagined repeated edge‑to‑edge with an infinite number of replicas. Image 3 shows two patterns with two different contents, and the one in dark dashed lines or one of its images under represents the same wallpaper on the following image 4, by disregarding the colors. Certainly a color is perceived subjectively whereas a wallpaper is an ideal object, however any color can be seen as a label that characterizes certain surfaces, we might think of a hexadecimal code of color as a label specific to certain zones. It may be added that a well‑known theorem deals with colors.
Groups are registered in the catalog by examining properties of a parallelogram, edge‑to‑edge with its replicas. For example its diagonals intersect at their common midpoints, center and symmetry point of any parallelogram, not necessarily symmetry point of its content. Other example, the midpoint of a full side shared by two patterns is the center of a new repetitive parallelogram formed by the two together, center which is not necessarily symmetry point of the content of this double parallelogram. Other possible symmetry point, two patterns symmetric one to the other with respect to their common vertex form together a new repetitive surface, the center of which is not necessarily symmetry point of its content.
Certain rotational symmetries are possible only for certain shapes of pattern. For example on image 2, a Pythagorean tiling is sometimes called pinwheel tilings because of its rotational symmetry of 90 degrees about the center of a tile, either small or large, or about the center of any replica of tile, of course. Also when two equilateral triangles form edge‑to‑edge a rhombic pattern, like on image 4 or 5 (future image 5), a rotational symmetry of 120 degrees about a vertex of a 120° angle, formed by two sides of pattern, is not always a symmetry point of the content of the regular hexagon formed by three patterns together sharing a vertex, because it does not always contain the same motif. | 1 | Crystallography |
Micelles are composed of surfactant, or detergent, monomers with a hydrophobic moiety, or tail, on one end, and a hydrophilic moiety, or head group, on the other. The polar head group may be anionic, cationic, zwitterionic, or non-ionic. When the concentration of a surfactant in solution reaches its critical micelle concentration (CMC), it forms micelles which are aggregates of the monomers. The CMC is different for each surfactant, as is the number of monomers which make up the micelle, termed the aggregation number (AN). Table 1 lists some common detergents used to form micelles along with their CMC and AN where available.
Many of the characteristics of micelles differ from those of bulk solvents. For example, the micelles are, by nature, spatially heterogeneous with a hydrocarbon, nearly anhydrous core and a highly solvated, polar head group. They have a high surface-to-volume ratio due to their small size and generally spherical shape. Their surrounding environment (pH, ionic strength, buffer ion, presence of a co-solvent, and temperature) has an influence on their size, shape, critical micelle concentration, aggregation number and other properties.
Another important property of micelles is the Kraft point, the temperature at which the solubility of the surfactant is equal to its CMC. For HPLC applications involving micelles, it is best to choose a surfactant with a low Kraft point and CMC. A high CMC would require a high concentration of surfactant which would increase the viscosity of the mobile phase, an undesirable condition. Additionally, a Kraft point should be well below room temperature to avoid having to apply heat to the mobile phase. To avoid potential interference with absorption detectors, a surfactant should also have a small molar absorptivity at the chosen wavelength of analysis. Light scattering should not be a concern due to the small size, a few nanometers, of the micelle.
The effect of organic additives on micellar properties is another important consideration. A small amount of organic solvent is often added to the mobile phase to help improve efficiency and to improve separations of compounds. Care needs to be taken when determining how much organic to add. Too high a concentration of the organic may cause the micelle to disperse, as it relies on hydrophobic effects for its formation. The maximum concentration of organic depends on the organic solvent itself, and on the micelle. This information is generally not known precisely, but a generally accepted practice is to keep the volume percentage of organic below 15–20%. | 0 | Chromatography + Titration + pH indicators |
After 125 years of study, 1,3,5-trinitrobenzene yielded a second polymorph. The usual form has the space group Pbca, but in 2004, a second polymorph was obtained in the space group Pca2 when the compound was crystallised in the presence of an additive, trisindane. This experiment shows that additives can induce the appearance of polymorphic forms. | 1 | Crystallography |
In crystallography and the theory of infinite vertex-transitive graphs, the coordination sequence of a vertex is an integer sequence that counts how many vertices are at each possible distance from . That is, it is a sequence
where each is the number of vertices that are steps away from . If the graph is vertex-transitive, then the sequence is an invariant of the graph that does not depend on the specific choice of . Coordination sequences can also be defined for sphere packings, by using either the contact graph of the spheres or the Delaunay triangulation of their centers, but these two choices may give rise to different sequences.
As an example, in a square grid, for each positive integer , there are grid points that are steps away from the origin. Therefore, the coordination sequence of the square grid is the sequence
in which, except for the initial value of one, each number is a multiple of four.
The concept was proposed by Georg O. Brunner and Fritz Laves and later developed by Michael O'Keefe. The coordination sequences of many low-dimensional lattices and uniform tilings are known.
The coordination sequences of periodic structures are known to be quasi-polynomial. | 1 | Crystallography |
Bromocresol purple (BCP) or 5′,5″-dibromo-o-cresolsulfophthalein, is a dye of the triphenylmethane family (triarylmethane dyes) and a pH indicator. It is colored yellow below pH 5.2, and violet above pH 6.8. In its cyclic sulfonate ester form, it has a pK value of 6.3, and is usually prepared as a 0.04% aqueous solution. | 0 | Chromatography + Titration + pH indicators |
In liquid chromatography:
* Charged aerosol detector electrically charged aerosol is used for the detection of non-UV-absorbing chargeable molecules, especially saccharides and lipids
* Evaporative light scattering detector evaporating non volatile solutes inside a volatile mobile phase for universal detection. used for saccharides and lipids and other non-UV-absorbing molecules
In gas chromatography:
* Flame ionization detector which uses ionizing flame to detect most hydrocarbon molecules
* Flame photometric detector which uses atomizing flame to get light emitted from specific elements to detect and quantify them
* Nitrogen Phosphorus Detector a thermionic detector with photometeric detection, sensitive specifically to nitrogen and phosphorus hydrocarbons
* Atomic-emission detector is a hyphenation between gas chromatography and atomic emission spectrophotometer for detection of elements.
In all types of chromatography:
* Mass spectrometer is in fact hyphenation between the separative instrument and a mass spectrometry instrument to get information on the molecular weight or atomic weight of the solute. In the advanced mass spectrometry technologies there is information on solutes structure and even chemical properties. The hyphenation between ultra high performance chromatography with high resolution mass spectrometers revolutionalized entire new scientific fields of research and application, such as toxicology, proteomics, lipidomics, genomics, metabolomics and metabonomics. | 0 | Chromatography + Titration + pH indicators |
"European Parliament and Council Directive 94/36/EC of 30 June 1994 on colours for use in foodstuffs" harmonized rules and approved Sunset Yellow FCF for use in foodstuffs in the whole of the European Union. Before that time, approved amounts was up to each country, but naming and composition was standardized.
Sunset yellow FCF was not approved in Norway before 2001. That was the time when the 94/36/EC directive of 1994 was included in EFTA (now EEC) rules and came into effect, after years of delaying tactics from the Norwegian side and a heated political debate.
In 2008, the Food Standards Agency of the UK called for food manufacturers to voluntarily stop using six food additive colours, tartrazine, allura red, ponceau 4R, quinoline yellow WS, sunset yellow and carmoisine (dubbed the "Southampton 6") by 2009, and provided a document to assist in replacing the colors with other colors.
An EU regulation came into effect in 2010 mandating that food manufacturers include a label on foods containing the Southampton 6 stating: "may have an adverse effect on activity and attention in children". | 0 | Chromatography + Titration + pH indicators |
o-Cresolphthalein is a phthalein dye used as a pH indicator in titrations. It is insoluble in water but soluble in ethanol. Its solution is colourless below pH 8.2, and purple above 9.8. Its molecular formula is CHO. It is used medically to determine calcium levels in the human body, or to synthesize polyamides or polyimides. | 0 | Chromatography + Titration + pH indicators |
If half of the tetrahedral sites of the parent FCC lattice are filled by ions of opposite charge, the structure formed is the zincblende crystal structure. If all the tetrahedral sites of the parent FCC lattice are filled by ions of opposite charge, the structure formed is the fluorite structure or antifluorite structure. If all the octahedral sites of the parent FCC lattice are filled by ions of opposite charge, the structure formed is the rock-salt structure. | 1 | Crystallography |
Advantages of HPTLC:
* Provides straightforward information about effects arising from individual compounds in complex or natural samples separated in parallel.
* Combines chromatographic separation with effect-directed detection using enzymatic or biological assays.
* Helps to select important compounds from a sample for further characterization using high-resolution mass spectrometry.
* Offers unique benefits such as super-hyphenation, minimum sample preparation requirements, detection of multi-modulating compounds, and distinguishing agonistic versus antagonistic effects. | 0 | Chromatography + Titration + pH indicators |