Determination of polar pesticides with atmospheric pressure chemical ionisation mass spectrometry-mass spectrometry using methanol and/or acetonitrile for solid-phase desorption and gradient liquid chromatography

Thirty-seven polar pesticides, mainly triazines, phenylurea herbicides and phenoxy acids, were determined by LC-atmospheric pressure chemical ionisati on MS-MS with methanol and acetonitrile as the organic modifiers. For most pesticides, detection limits were the same irrespective of the modifier. Ho wever, for the phenylurea herbicides, propachlor, carbetamide, triadimefon, triadimenol, triethylcitrate, benzothiazole and metazachlor, the results w ere much poorer in the presence of acetonitrile; in several cases, no meani ngful results were obtained at all. When carrying out trace enrichment of 1 00 mi water samples on a 10X2 mm I.D. solid-phase extraction precolumn cont aining a polymeric sorbent, rapid desorption with a small volume of pure or ganic solvent and the introduction of a T-piece in between the solid-phase extraction precolumn and the analytical column was necessary. ALiquots of 3 00 mu l of acetonitrile were optimal for the complete desorption of all ana lytes from the sorbent. With methanol as the modifier and when using an ide ntification criterion of three ions, the detection limits for most analytes , in the full-scan mode, were 10-100 ng/l. The linearity of the procedure, which was tested at the 0.1 and 1 mu g/l levels, was satisfactory in the po sitive, but not in the negative ionisation mode. The procedures were used t o analyse surface water samples. (C) 1999 Elsevier Science B.V. All rights reserved.