Separation of lidocaine and its metabolites by capillary electrophoresis using volatile aqueous nonaqueous electrolyte systems

The separation of the basic drug lidocaine and six of its metabolites has b een investigated both by using volatile aqueous electrolyte system, at low pH and by employing non-aqueous electrolyte systems. In aqueous systems, th e best separation of the compounds under the investigated conditions was ac hieved by using the electrolyte 60 mM trifluoroacetic acid (TFA)/triethylam ine (TEA) at pH 2.5 containing 15% methanol. With this electrolyte, all sev en compounds were well separated with high efficiency and migration time re peatability. The separations with bare fused-silica capillaries and polyacr ylamide-coated capillaries were compared with higher separation efficiency with the latter. On the other hand, near baseline separation of all the sev en compounds was also obtained by employing the non-aqueous electrolyte, 40 mM ammonium acetate in methanol and TFA (99:1, v/v), with comparable migra tion time repeatability but lower separation efficiency relative to the aqu eous system.