Mobile phase variations in thermospray liquid chromatography-mass spectrometry of pesticides

The effect of four different mobile phase compositions with reversed-phase methanol-water (50:50) + 0.05 M ammonium acetate, methanol-water (50:50) + 0.05 M ammonium formate, acetonitrile-water (50:50) + 0.05 M ammonium acetate and acetonitrile-water (50:50) + 0.05 M ammonium formate were compared in filament-on thermospray liquid chromatography-mass spectrometry for the determination of carbamate and chlorotriazine pesticides. In the positive-ion mode, M + H]+ and M + NH4]+ were generally the base peaks for the chlorotriazines and the carbamates, respectively. Depending on the mobile phase used, other adduct ions obtained corresponded to M + CH3CN + H]+, M + CH3OH + NH4]+, M + CH3COONH4 + NH4 - 2H2O]+, M + CH3CN + NH4]+, M + CH3COONH4 + H - H2O]+ and the dimer 2M + H]+. In the negative-ion mode, M - H]- and adducts with the ionizing additive M + CH3COO]- or M + HCOO]- were obtained. Other ions for the carbamates carbaryl and oxamyl corresponded to M - CONHCH3 + CH3COOH]- and M - CON(CH3)2 + HCOO]-, respectively. The variation of mobile phase composition provides additional structural information in thermospray liquid chromatography-mass spectrometry with no appreciable loss of sensitivity. Applications are reported for the determination of carbamate and chlorotriazine pesticides at the ng/g level in spiked and real soil samples, respectively.