Chromatography A Separation Technique

Chromatography—A separation technique producing a qualitative record of the relative amounts of components, a chromatogram. HPLC modes include partition and adsorption (polarity), GPC or SEC (size), ion exchange (charge), or affinity (compound-specific retention). 

Adsorption chromatography A separation technique in which a solute equilibrates between the eluent and the surface of a finely divided adsorbed solid. 

A wide range of stabilizers in plastics is identified commercially using high performance liquid chromatography, a separation technique based on the distrihu-tion of compounds between two phases known as the stationary phase and mohUe phase. The stationary phase comprises a thin layer created on the surface of fine particles and the mobile phase comprises the liquid flowing over the particles. Each component in a sample has a different distribution equilibrium depending on its solubility in the phases and/or molecular size. As a result, the components move at different speeds over the stationary phase and are thereby separated from each other. The sample is dissolved using a suitable solvent, a non solvent such as methanol is added, and the extract presented to the HPLC. 

Gas chromatography, a separation technique based on the distribution of gaseous compounds between a mobile gaseous phase and a stationary adsor-bant phase. The method was developed by Martin and James in 1952 [A.J.P.Martin in R.Porter (ed.) Gas Chromatography in Biology and Medicine. A... 

Optical chromatography, a separation technique involving the use of a radiation force and a medium flow, has been used to carry out immunoassays. The radiation force induced on a particle when irradiated by a laser beam and the force induced by the medium flow are related to the diameter of the particle. Optical chromatography allows separation of free Ab-particles without Ag from the Ab particles bound to Ag taking into account that particles coated with Ab agglutinate in the presence of Ag. The concentration of Ag can be calculated through the ratio of bound to free particles [132]. 

Affinity chromatography. A separation technique that exploits the high biological specificity and affinity of specific naturally occurring proteins for the analyte. 

The particle size (often nano) and polydispersion are usually confirmed via scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS) or hydrodynamic chromatography, a separation technique that keeps apart the particles on the basis of the size sometimes DLS and SEM data are not directly comparable (SEM images are collected from dried samples while DLS measurements are in solution and a swelling effect occurs) but the trends of growth of the nanoparticles are similar for the two methods. 

Liquid chromatography is a separation technique based on the selective adsorption on a solid, siiica or alumina for example, or a mixture of the two, of the different components of a liquid mixture. 

Mixtures can be identified with the help of computer software that subtracts the spectra of pure compounds from that of the sample. For complex mixtures, fractionation may be needed as part of the analysis. Commercial instmments are available that combine ftir, as a detector, with a separation technique such as gas chromatography (gc), high performance Hquid chromatography (hplc), or supercritical fluid chromatography (96,97). Instmments such as gc/ftir are often termed hyphenated instmments (98). Pyrolyzer (99) and thermogravimetric analysis (tga) instmmentation can also be combined with ftir for monitoring pyrolysis and oxidation processes (100) (see Analytical methods, hyphenated instruments). 

A brief description is given of the way in which modern liquid chromatography has been developed from classical techniques. The important components of a high performance liquid chromatograph are introduced and the method is compared with gas chromatography as a separation technique. 

Trathnigg, B., Kollroser, M., Rappel, C. (2001). Liquid exclusion adsorption chromatography, a new technique for isocratic separation of nonionic surfactants. III. Two-dimensional separation of fatty alcohol ethoxylates. J. Chromatogr. A 922(1-2), 193-205. 

Either gas chromatography (GC) or liquid chromatography (LC) can be used as a separation technique coupled with a variety of detection methods. Mass spectrometry (MS) is one of the most popular means of detection. When using GC-MS, a capillary column should be used, while any suitable LC column can be used for LC-MS. It is advisable to obtain a print-out of the chromatogram so that the shapes of individual peaks can be assessed. Electronically produced data using integrators should be treated with some suspicion and always examined visually to check the selected baseline, start- and end-points of peak integration, etc. 

IUPAC defines supercritical chromatography as a separation technique in which the mobile phase is kept above (or relatively close to) its critical temperature and pressure. 

Ettre LS. Chromatography the separation technique of the twentieth century. In Issaq HJ (ed.), A Century of Separation Science. New York Marcel Dekker, Inc. 2002, pp. 1-17. 

Y. Bereznitski, R. Thompson, E. O Neill and N. Grinberg, Thin-layer chromatography—a useful technique for the separation of enantiomers, J. AOAC Int., 84(4) (2001) 1242-1251. 

Give a general definition of chromatography that would apply to all types and configurations. (To say that it is a separation technique is important but not sufficient.)... 

Chromatography is a separate technique in which mixture components are separated based on the differences in the extent of their interaction with two phases, a mobile phase and a stationary phase. 

The first two groups have been collectively termed as Gas Chromatography .Its phenomenal growth at almost logarithmic pace may be attributed to its unparalleled potential in resolving components of a complex mixture. Gas chromatography fundamentally is a separation technique that not only essentially provides prima facie indentification of a compound but also caters for quantitative estimation after due calibration. 

One of the major advantages of CE as a separation technique is the wide variety of separation modes available. Analytes can be separated on the basis of charge, molecular size or shape, pi, or hydrophobicity. The same CE instrument can be used for zone electrophoresis, IEF, sieving separations, isotachophoresis, and chromatographic techniques such as MEKC and capillary electrokinetic chromatography. This section provides a brief description of each separation mode. Zone electrophoresis, IEF, and sieving are the primary modes used for protein separations, and these will be discussed in detail in the following sections. 

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