Identification of fenthion and temephos and their transformation products in water by high-performance liquid chromatography with diode array detection and atmospheric pressure chemical ionization mass spectrometric detection

Two organophosphorus pesticides, fenthion and temephos were oxidized with N-bromosuccinimide (NBS) in order to obtain the oxidated analogues which are the activated form of the pesticides. Analysis of the non-oxidized solution containing the pesticides, and two oxidized solutions which differed in the amount of NBS added was performed with both LC-diode array detection and NMR to confirm the presence of the degradation products. LC-atmospheric pressure chemical ionization-MS was used to unequivocally identify all the transformation products formed. With this technique it was possible to identify oxo derivatives, sulfoxides and isomers of both fenthion and temephos. Fenthion and its transformation products were characterized with both positive and negative mode of ionization whereas temephos was analyzed at an extraction voltage of 20 V to gain in sensitivity and at 40 V to enhance fragmentation. With both fenthion and temephos, the isomeric forms of these pesticides, the oxons and the sulfoxides eluted before the parental pesticide. It was observed that an increase of NBS produced fenthion sulfoxide oxon and temephos dioxon while the parental pesticides disappeared from these samples. Tn the case of temephos, the oxidation of this pesticide with NBS reproduce environmental conditions, since these same transformation products were also found in environmental waters that had been treated with temephos. (C) 1997 Elsevier Science B.V.