CHARACTERIZATION OF ISOMERIC SULFONAMIDES USING CAPILLARY ZONE ELECTROPHORESIS COUPLED WITH NANO-ELECTROSPRAY QUASI-MS MS/MS/

The application of capillary electrophoresis/nano-electrospray mass sp ectrometry to the multi-residue analysis of a large number of sulfonam ide antibiotics in milk samples is reported. Tandem mass spectrometric (MS/MS) techniques including precursor ion scans and multiple reactio n monitoring were used to identify residues at the low ppb level to th e ppt level. Three pairs of isomeric sulfonamides were targeted that d iffer only in the positions of the nitrogen and oxygen atoms in the he terocyclic aromatic rings of the molecules. Conventional MS/MS analysi s yielded no isomer-specific ions. Therefore, a quasi-MS/MS/MS method was applied to overcome these limitations. In-source collision-induced dissociation (CID) was used as a quasi-MS/MS stage to generate ions a rising from the heteroaromatic amine moiety. In a second MS/MS step th ese ions were isolated and made to undergo CID in the collision quadru pole to yield isomer-specific ions. Examples of the application of the se methodologies to the analysis of milk extracts are illustrated. (C) 1997 by John Wiley & Sons, Ltd.