A nonaqueous capillary electrophoresis/electrospray mass spectrometry method for the separation of lidocaine (LID) and two of its metabolites, monoethylglycinexylidide (MEGX) and glycinexylidide (GX), has been developed. The separation medium was: 70 mM ammonium formate and 2.0 M formic acid in acetonitrile/methanol (60:40 v/v). With a sheath liquid of methanol/water (80:20 v/v) containing 2% formic acid and positive ion detection, reproducible determinations (8-11% relative standard deviation (RSD)) of lidocaine and its metabolites were performed in spiked human plasma. The limits of detection (LODs) were between 69.1 and 337 nM. The influences of sheath liquid composition, nebulizing gas pressure and drying gas temperature on the separation were examined.

The separation of the basic drug lidocaine and six of its metabolites has been investigated both by using volatile aqueous electrolyte system, at low pH and by employing non-aqueous electrolyte systems. In aqueous systems, the best separation of the compounds under the investigated conditions was achieved by using the electrolyte 60 mM trifluoroacetic acid (TFA)/triethylamine (TEA) at pH 2.5 containing 15% methanol. With this electrolyte, all seven compounds were well separated with high efficiency and migration time repeatability. The separations with bare fused-silica capillaries and polyacrylamide-coated capillaries were compared with higher separation efficiency with the latter. On the other hand, near baseline separation of all the seven compounds was also obtained by employing the non-aqueous electrolyte, 40 mM ammonium acetate in methanol and TFA (99:1, v/v), with comparable migration time repeatability but lower separation efficiency relative to the aqueous system.

A method for the separation of lidocaine and six of its metabolites in plasma has been developed. Separation was performed using a buffer consisting of 35 mM phosphate/Tris pH 3.0, 6 mM cetyltrimetylammoniumbromid (CTAB) and 9% (v/v) methanol. The key variables, CTAB and methanol concentrations, were optimized by the application of a factorial design. Rinsing the capillaries with ethanol between runs resulted in highly reproducible migration times, relative standard deviation 0.69%. Under the conditions applied, the seven analytes could be separated with high efficiency and resolution within 8.1 min. Overall performance, as demonstrated in validation experiments, was excellent. ©1999 John Wiley & Sons, Inc. J Micro Sep 11: 620–626, 1999

Comparison of the features of arthroscopic synovial biopsies with biopsy samples obtained at surgery