Optimisation of a simultaneous separation of sulphonamides, dihydrofolate reductase inhibitors and beta-lactam antibiotics by capillary electrophoresis

There are many high-performance liquid chromatographic assays for the determination of sulphonamides, dihydrofolate reductase inhibitors and beta-lactam antibiotics individually in food products. Recently, some capillary electrophoresis (CE) assays for these drugs have appeared. Sulphonamides plus dihydrofolate reductase inhibitors are readily separated by capillary zone electrophoresis (CZE) and micellar electrokinetic capillary chromatography (MECC) can separate beta-lactams. However, if CE is to prove its value over HPLC techniques in practice then its intrinsic high resolution must be exploited fully. A combination of a sulphonamide-dihydrofolate reductase inhibitors separation by CZE with a MECC assay of beta-lactams would be advantageous in the screening of food products for veterinary drug residues, saving both time and effort. The analysis of all three classes of drugs, in a single run, was tested using our established beta-lactam MECC conditions, but this gave only a partial separation, with a very crowded region. A Box-Behnken factorial design was used to optimise this separation. It was carried our parallel with the ''traditional trial and error procedure'', based on our knowledge of the individual CE separations. Both methods arrived at a remarkably similar set of conditions. The final separation produced 25 peaks, within which, were 30 compounds, the separation taking 25 min.