TRACE-LEVEL DETERMINATION OF PESTICIDE-RESIDUES USING ONLINE SOLID-PHASE EXTRACTION-COLUMN LIQUID-CHROMATOGRAPHY WITH ATMOSPHERIC-PRESSURE IONIZATION MASS-SPECTROMETRIC AND TANDEM MASS-SPECTROMETRIC DETECTION

Column liquid chromatography (LC) with pneumatically assisted electros pray (PA-ESP) or atmospheric pressure chemical ionization (APCI) follo wed by (tandem) mass spectrometry (MS or MS-MS) was used for the analy sis of a test mixture of 17 pesticides. In order to achieve low-ng/l d etection limits, solid-phase extraction (SPE) of a 100-ml aqueous samp le on a small cartridge packed with a hydrophobic sorbent was used. Th e LC set-up was coupled on-line to the MS part of the system. The comp lete analysis was automated by means of a gradient controller and a Pr ospekt valve switching, solvent selection and cartridge exchange unit. When using SPE-LC with either APCI or PA-ESP, the detection limits of 15 (out of the 17) pesticides in tap water were 0.007-3 mu g/l in the full-scan and 0.1-200 ng/l in the SIM mode, with an analysis time of 65 min. Fenchlorphos and bromophos-ethyl could not be detected by eith er ionization method. APCI full-scan spectra showed much less sodium a nd acetonitrile/water cluster adducts than PA-ESP spectra. Negative io n (NI) operation was less sensitive for the majority of the compounds tested (73 in total), but several organophosphorus pesticides, nitroph enols and chlorophenols only gave a response in the NI mode. PA-ESP-MS -MS and APCI-MS-MS gave similar product-ion spectra from protonated mo lecules; an MS-MS library was built for more than 60 pesticides and th eir degradation products, at constant settings of collision gas pressu re (argon, 2.0x10(-3) Torr) and collision energy (25 eV). The library was successfully used for searching product-ion spectra from SPE-LC-AP CI-MS-MS at low levels (10 ng/l) in tap water and for the identificati on of atrazine in surface water (estimated concentration 0.25 mu g/l).