COMPARISON OF AUTOMATED ONLINE SOLID-PHASE EXTRACTION FOLLOWED BY LIQUID-CHROMATOGRAPHY MASS-SPECTROMETRY WITH ATMOSPHERIC-PRESSURE CHEMICAL-IONIZATION AND PARTICLE-BEAM MASS-SPECTROMETRY FOR THE DETERMINATIONOF A PRIORITY GROUP OF PESTICIDES IN ENVIRONMENTAL WATERS

Atmospheric pressure chemical ionization (APCI) in both positive and n egative ionization modes and particle beam (PB) in electron impact (EI ) and chemical ionization in positive (PCI) and negative (NCI) modes m ass spectrometry (MS) coupled to high-performance liquid chromatograph y (HPLC) are compared in the determination of a group of pesticides. T he method was combined with an automated on-line solid-phase extractio n (SPE) step by preconcentrating 200 ml of sample through C-18 pre-col umns in order to perform the determination of these pesticides at low levels. Calibration graphs were constructed with time-scheduled select ed ion monitoring (STM) and using the internal standard method; for AP CI under positive ion (PI) mode limits of detection (LODs) were betwee n 0.8 and 4 ng l(-1) and under negative ion (NI) mode of operation, be tween 4 and 20 ng l(-1); for PB the LODs were between 0.05 to 0.2 mu g l(-1) under EI conditions and from 0.02 to 0.1 mu g l(-1) under chemi cal ionization in both positive and negative acquisition modes. The st udy demonstrates the higher sensitivity of HPLC-APCI-MS compared with HPLC-PB-MS and the potential of both techniques for confirming the pre sence of contaminants in environmental matrices. The developed methods were validated by participating in Aquacheck inter-laboratory exercis es. (C) 1998 Elsevier Science B.V.