Temperature and extraction voltage effect on fragmentation of organophosphorus pesticides in liquid chromatography atmospheric pressure chemical ionization mass spectrometry

Liquid chromatography coupled to mass spectrometry with atmospheric pressure chemical ionization is an excellent technique for analysis of organophosphorus pesticides which are not gas chromatography amenable or pose problems with the use of diode array detection or an iomspray interface. This study was directed to evaluate the effect of the probe temperature and extraction voltage on sensitivity and fragmentation of several organophosphorus pesticides. Five different temperatures, varying from 100 to 500 degrees C and five extraction voltages, from 10 to 60 V were applied. In first instance, all the studied compounds were characterized at 3-5 different ions under each experimental condition. From this qualitative information, together with the relative abundances of each ion, the theory of information was applied to objectively distinguish the condition(s) that gave more structural information. For pesticides of the parathion group, an intense fragmentation was observed at all extraction voltages, while sensitivity decreased with increasing extraction voltage. In general, higher structural information was obtained when increasing the extraction voltage, compared to an increase of temperature. However, temperatures of 400-500 degrees C produced the highest sensitivity for the majority of the pesticides. Extraction voltages of 40 to 60 V produced ions at low m/z, which could not be used for identification purposes. The optimum conditions, with regard to best sensitivity and structural information were used to calculate the recoveries of the studied pesticides. Two solid-phase extraction phases, LiChrolut EN and Isolute ENV, were used to preconcentrate 200 ml of groundwater spiked at levels of 0.2 mu g/l. Problems arose during attempts to recover those compounds which exhibit high vapor pressure. (C) 1998 Elsevier Science B.V.