Use of a partial filling technique and reverse migrating micelles in the study of N-methylcarbamate pesticides by micellar electrokinetic chromatography-electrospray ionization mass spectrometry

This study describes three ways to couple micellar electrokinetic chromatog raphy (MEKC) on-line with electrospray ionization mass spectrometry (ESI-MS ) for the analysis of N-methylcarbamate pesticides. The methods involved th e use of a partial filling (PF) technique under basic conditions and the us e of reverse migrating micelles (RMMs) under acidic and basic conditions. T he use of RMMs in basic electrolyte solutions required coated capillaries w ith low electroosmotic flows, and capillaries coated with anionic poly(sodi um 2-acrylamide-2-methylpropanesulfonate) were selected for the purpose. Be fore the on-line MEKC-ESI-MS coupling, the MEKC and MS conditions were sepa rately optimized under off-line conditions. The methods were compared in te rms of detection limits and the stability of the electrospray process. The PF method offered good separation but poorer stability of the electrospray relative to the other methods. A more stable electrospray performance was o btained with use of RMMs in acidic electrolyte solutions, but some of the a nalytes were protonated and could not be detected due to the increase in th eir retention factors. However, with the use of anionic polymer-coated capi llaries and RMMs at pH 8.5, all analytes were successfully separated. The h igh-salt stacking method was applied to improve the sensitivity of MEKC-ESI -MS and the detection limits were in the range of 0.04-2.0 mug/ml. (C) 2001 Elsevier Science B.V. All rights reserved.