IDENTIFICATION OF PESTICIDES BY LIQUID-CHROMATOGRAPHY PARTICLE-BEAM MASS-SPECTROMETRY USING ELECTRON IONIZATION AND CHEMICAL-IONIZATION

Liquid chromatography-mass spectrometry (LC-MS) with a particle beam ( PB) interface is used to separate and identify a group of pesticides. The mass spectra obtained under the different ionization modes, electr on ionization (EI) and positive and negative chemical ionization (PCI and NCI) are compared. The operating conditions under each mode, deter mined by studying the influence on the ion abundance of the ion source temperature of the EI mode, and the gas pressure and ion source tempe rature in the methane CI were optimized. EI was more sensitive than PC I and NCI and of the latter two modes, NCI gave higher responses, espe cially for organophosphorus compounds. When on-line solid-phase extrac tion-LC-PB-MS was applied to real samples, limits of detection in full scan mode were in the range of 0.5 and 10 mu g l(-1) for EI. The anal ysis of real samples by on-line solid-phase extraction-LC-PB-MS enable d EI detection of one of the pesticides studied and confirmation by PC I and NCI. The combined EI/CI information also enabled the detection o f some non-target compounds. (C) 1998 Elsevier Science B.V.