Application of thermospray liquid chromatography/mass spectrometry for determination of organophosphorus pesticides and trialkyl and triaryl phosphates

Abstract

The characterization of several organophosphorus compounds was achieved by utilizing positive and negative ion ‘filament‐on’ thermospray liquid chromatography/mass spectrometry. In the positive ion mode, the base peak was [M + NH₄]⁺ for all the studied compounds, while in the negative ion mode the organophosphorus pesticides exhibited different fragmentation behaviour, such as electron capture, dissociative electron capture and anion attachment. The positive ion mode showed, for all the organophosphorus compounds, higher sensitivity than the negative ion mode. In the positive ion mode, detection limits at the low nanogram level were achieved for the trialkyl and triaryl phosphates, similar to gas chromatography/positive chemical ionization mass spectrometry with ammonia as reagent gas. The organophosphorus pesticides exhibited detection limits slightly lower than the phosphates, but with values similar to those previously observed in direct liquid introduction liquid chromatography/negative chemical ionization mass spectrometry. Applications of positive and negative ion analysis are reported for the determination of malathion in a fish sample.