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 pr essure chemical ionization is an excellent technique for analysis of o rganophosphorus pesticides which are not gas chromatography amenable o r pose problems with the use of diode array detection or an iomspray i nterface. 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, var ying from 100 to 500 degrees C and five extraction voltages, from 10 t o 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 abunda nces of each ion, the theory of information was applied to objectively distinguish the condition(s) that gave more structural information. F or pesticides of the parathion group, an intense fragmentation was obs erved at all extraction voltages, while sensitivity decreased with inc reasing extraction voltage. In general, higher structural information was obtained when increasing the extraction voltage, compared to an in crease of temperature. However, temperatures of 400-500 degrees C prod uced the highest sensitivity for the majority of the pesticides. Extra ction voltages of 40 to 60 V produced ions at low m/z, which could not be used for identification purposes. The optimum conditions, with reg ard to best sensitivity and structural information were used to calcul ate the recoveries of the studied pesticides. Two solid-phase extracti on phases, LiChrolut EN and Isolute ENV, were used to preconcentrate 2 00 ml of groundwater spiked at levels of 0.2 mu g/l. Problems arose du ring attempts to recover those compounds which exhibit high vapor pres sure. (C) 1998 Elsevier Science B.V.