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

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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 + NH 4] + 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 + CH 3CN + H] +, [M + CH 3OH + NH 4] +, [M + CH 3COONH 4 + NH 4 − 2H 2O] +, [M + CH 3CN + NH 4] +, [M + CH 3COONH 4 + H − H 2O] + and the dimer [2M + H] +. In the negative-ion mode, [M − H] − and adducts with the ionizing additive [M + CH 3COO] − or [M + HCOO] − were obtained. Other ions for the carbamates carbaryl and oxamyl corresponded to [M − CONHCH 3 + CH 3COOH] − and [M − CON(CH 3) 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.