HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY THERMOSPRAY MASS-SPECTROMETRY OF 10 SULFONAMIDE ANTIBIOTICS - ANALYSIS IN MILK AT THE PPB LEVEL

Ten sulfonamide antibiotics including sulfanilamide (SNL), sulfamethazine (SMZ), sulfamethizole (SMTZ), sulfachloropyridazine and sulfaquinoxaline (SQX), were analyzed by thermospray (TSP) mass spectrometry on-line with a high-performance liquid chromatography-UV detection system. Except for the pairs SMZ-SMTZ and sulfadimethoxine-SQX, the standards were resolved in both the UV and TSP profiles. Co-eluting compounds could be differentiated in TSP by their different relative molecular masses. The [M + H]+ ion was the base peak for all the standards except SNL, which showed an [M + NH4]+ ion. Collision-induced dissociation of the [M + H]+ ions afforded daughter ion spectra characterized by common ions at m/z 92, 108 and 156, and ions derived from the amine substituent ([MH - 155]+). TSP detection limits [signal-to-noise ratio (S/N) > 3] were below 20 ng (scan mode), 2 ng (selected reaction monitoring, daughter ions from [M + H]+) and 400 pg (selected ion monitoring). UV detection limits were ca. 2 ng (S/N > 5). Results obtained from the multi-residue analysis of spiked cow milk samples at the low ng/ml level are presented.