Evaluation of the van Deemter equation in terms of open-ended flow to chromatography

Plate theory and adsorption theory are the main tools available for understanding chromatographic experiments. Both theories predict a Gaussian distribution of solute molecules within the tubular system. However, Gaussian concentration distributions are observed predominantly at slow linear flow rates, while asymmetric concentration distributions are observed at the linear flow rates most used in chromatography. Allegedly, this asymmetry originates from an inhomogeneous distribution of grain sizes in the column and column overload. However, it is an experimental fact that the distribution of chemicals within an injected volume of solute changes as a function of time, while the response is measured simultaneously. Accordingly, the obtained signal cannot be compared to the theory before some type of time-based deconvolution of the data has been performed. Adjustments to high-performance liquid chromatography data were thus proposed through empirical equations that describe the relevant time values, peak height, peak area, and parameters of the van Deemter equation. It was proposed that the transfer of solute from the front to the rear part of the pulse during laminar open-ended flow occurs at rate that depends on the linear flow rate, and to a lesser extent, on properties of the response function.