Capillary electrophoresis separation of sulphonamides and dihydrofolate reductase inhibitors

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Abstract
Twenty‐two sulphonamides and three dihydrofolate reductase inhibitors (DHFR) were included in this study. At pH 7.5, eighteen drugs were resolved in 22 min. Above pH 7.5 the DHFR are not resolved and the pH range of 7‐7.5 was found to be optimal. Around pH 7, where the degree of ionization of the SFA is highly variable, pKa and migration time are strongly correlated. Increasing phosphate buffer concentration from 25‐100 mM generally improves resolution but increases analysis times. A good correlation between analyte mobility and the ratio of net charge to molecular weight indicates that this ratio may be used as a quick guide to the possibility of separation of related compounds. Our secondary objective was to compare the lead time and effectiveness of CZE with LC. It is clear that method development is much more rapid in CZE but with a sufficiently diverse group of compounds, CZE can be incapable of providing a full analysis without gradient control. Nonionized compounds are not separated at one extreme, and excessively mobile species may not emerge in a reasonable time, or, may migrate to the wrong electrode.