Electromigration dispersion in capillary zone electrophoresis: Experimental validation of use of the Haarhoff–Van der Linde function

This paper provides experimental validation of the use of the Haarhoff–Van der Linde (HVL) peak fitting function to fit experimental capillary zone electrophoresis (CZE) electropherograms. The test mixtures were composed of paraquat over a five order of magnitude concentration range (1.2 μM to 120 mM) and 4-aminopyridine at constant concentration (0.53 mM) as internal standard. Peak descriptors and electrophoresis parameters were extracted reliably by a Gaussian function from 4 to 40 μM; by the HVL function from 120 μM to 4 mM; and by a triangular function from 4 to 120 mM. The HVL function can be used where there is significant peak asymmetry due to electromigration distortion (EMD) and the Gaussian contribution toward the peak variance is greater than 25%. The peak centre (a1) and the Gaussian variance (a2) of the paraquat peak are shown to be independent of concentration. Diffusion coefficients obtained from a2 for both analytes were found to be in good agreement with their theoretical values. For all peaks where the distortion coefficient (a3) can be extracted, this parameter is shown to be directly proportional to the sample loading, as predicted by EMD theory. For the 4-aminopyridinium ion, mobilities calculated from a3 and measured independently are in excellent agreement. These results show that the HVL function accurately describes the two major processes, diffusion and EMD, contributing to the variance during a CZE separation.