Theory, chromatography retention time/volume

It is possible to correct this ultra-simple approach with a Plate Theory model for the variation of peak width with retention time (volume), conveniently expressed via the capacity factor k. The derivation and final result are complex (Scott, http //www.chromatography-online.org/) and are not reproduced here. Instead, Figure 3.5 shows representative plots of Cp vs k for several values of N, calculated from this more realistic model. The values of N and k are of course those for the last-eluting peak, but this last peak will be different for different chromatographic detectors with different sensitivities. It is clear from Figure 3.5 that any chromatographic conditions that limit the k value for the last-detected peak will thus limit the peak capacity, particularly at lower values of k. ... 

A complete theory predicting retention times or volumes as function of molecular size has not yet been formulated for gel permeation chromatography. A specific column or set of columns is calibrated empirically to give such a relationship, by means of which a plot of amount of solute versus retention volume (the chromatogram figure below) can be changed into a molecular-size-distribution curve. Generally commercially available narrow... 

The applicability of the additive retention theory to capillary chromatography with modified adsorbents was demonstrated for the first time in paper [125]. This work used experimental data [126] on n-hep-tane retention on an alkaline treated glass capillary column, the walls of which were coated with squalane, as reported by Bruner and Carton [126]. The dependence of retention volume on the liquid phase content was shown to be linear, being in complete agreement with additive absorption-adsorption theory. 

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