Van-Deemter Curves in Ion Chromatography

Although the various HETP equations differ significantly from each other, 

Scott et al. [11] showed that, on the basis of their extensive experimental data, the dependence of the theoretical plate height H on the linear flow velocity may be satisfactorily described by the Van-Deemter equation in the range between 0.02 cm/s and 1 cm/s. In Scott s tests, porous silicas with four different particle sizes were employed as stationary phases, on which nine solute compounds were separated using six different eluant mixtures. 

Although the experimental data for H and v may be depicted by any hyperbolic function, not all of them provide a meaningful physical insight into the dispersion process. According to Scott et al. [11], the Van-Deemter equation in the form 

Instead of the total plate height H and the linear flow velocity v, often the reduced plate height, h. 

The graphical representation of In k as a function of In w (Fig. 2-6) is known in the literature as the Knox plot. The dependence of the curve s position on the retention of the compound is disadvantageous. Minima in this kind of illustration are only obtained for compounds having no retention (k = 0). 

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