Capillary electrophoresis methods for the separation of the basic compound lidocaine and its metabolites

Abstract: For the separation of the basic compound lidocaine and its metabolites a variety of capillary electrophoresis (CE) methods have been developed. This includes capillary zone electrophoresis (CZE), micellar electrokinetic chromatography (MEKC) and nonaqueous CE separations. The parameters affecting the separations were investigated and optimized.In CZE reproducible separations were obtained in both un-coated and polyacrylamide-coated fused silica capillaries using a TFA/TEA electrolyte at pH 2.5.The MEKC method: a low pH phosphate/Tris buffer containing the cationic surfactant cetyltrimethylammonium bromide (CTAB) was successfully validated in human plasma.A couple of nonaqueous methods were developed. One of the methods 70 mM ammonium formate and 2 M formic acid in acetonitrile/methanol (60:40 v/v) was used for capillary electrophoresis-electrospray mass spectrometry analysis. Reproducible determinations in human plasma were obtained. The sensitivity was improved compared to UV. The detection limits for lidocaine and the metabolites monoethylglycinexylidide (MEGX) and glycinexylidide (GX) were 69 nM, 130 nM and 337 nM respectively. Parameters such as sheath liquid composition, nebulizing gas pressure and drying gas temperature were considered.The results show that CE is a simple and powerful technique for the separation of basic compounds.