Concentration and separation of hypoglycemic drugs using solid-phase extraction-capillary electrophoresis

Solid-phase extraction-capillary electrophoresis (SPE-CE) is a technique whereby very dilute analytes may be selectively extracted from a sample matrix and concentrated on-line for analysis. This study describes the first phase in the development of a method exploiting this technique for the direct analysis of hypoglycemic drugs in urine. Effective separation and detection of six sulfonylurea drug standards at concentrations below the detection limit of conventional capillary electrophoretic techniques is shown to be attainable. Since surfactant interfered with the on-line concentration process, non-MEKC (micellar electrokinetic chromatography) separation conditions were defined. Using 250 mM borate/5 mM phosphate at pH 8.4, all drugs in a mixture at 285 ng/ml were effectively extracted, concentrated from an injected volume of 2.5 microliters, non-selectively desorbed with an organic-based elution buffer and electrophoretically resolved. Sample loading was found to be linear in the 0.12-1.9 microliters range and drugs in a volume of up to 190 microliters could be concentrated and detected with a sensitivity of approximately 5 ng/ml. Not only was resolution of the desorbed material uncompromised by the presence of the SPE-tip, but separation of glipizide and glyburide was observed despite the fact that these drugs were unresolved under the same separation conditions by standard capillary zone electrophoresis (CZE). From these results, it is clear that SPE-CE not only increases the sensitivity for detection but that selectivity may be altered due to chromatographic processes occurring on the solid-phase resin.