Theory, chromatography longitudinal diffusion

Golay equation 21, 611 gradient (LC) 490 height equivalent to a theoretical plate 11 longitudinal diffusion 16 mass transfer resistance 17 nonlinear chromatography SOS plate model 14 rate theory IS reduced parameters 78, 361, 611... 

Liquid-solid chromatography is representative of this theory because nonlinearity effects are usually appreciable. Mass transfer is fast and longitudinal diffusion effects may be ignored in describing the system. The net result is that the bands (zones) develop self-sharpening fronts and diffuse rear boundaries. It is because of this tailing that this technique is to be regarded... 

The open-tubular column or capillary column is the one most commonly used in gas chromatography (GC) today. The equation that describes dispersion in open tubes was developed by Golay [1], who employed a modified form of the rate theory, and is similar in form to that for packed columns. However, as there is no packing, there can be no multipath term and, thus, the equation only describes two types of dispersion. One function describes the longitudinal diffusion effect and two others describe the combined resistance to mass-transfer terms for the mobile and stationary phases. 

The rate theory examines the kinetics of exchange that takes place in a chromatographic system and identifies the factors that control band dispersion. The first explicit height equivalent to a theoretical plate (HETP) equation was developed by Van Deemter et al. in 1956 [1] for a packed gas chromatography (GC) column. Van Deemter et al. considered that four spreading processes were responsible for peak dispersion, namely multi-path dispersion, longitudinal diffusion, resistance to mass transfer in the mobile phase, and resistance to mass transfer in the stationary phase. 

Recently Desmet and Deridder transformed the effective medium theory (EMT), which applied thermal and electrical conductivity, to determine longitudinal diffusion in chromatography (71). EMT equations can be applied for fully porous, porous shell, spherical, and cylindrical particles. The theory considers the column as a binary medium, which consists of an interstitial void with a volumetric fraction Se and particles with a volumetrical fraction of 1- e. ... 

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