Ultra-trace-level determination of polar pesticides and their transformation products in surface and estuarine water samples using column liquid chromatography-electrospray tandem mass spectrometry

A method is developed for the determination of polar pesticides and their t ransformation products [atrazine, deethylatrazine, deisopropylatrazine, hyd roxyatrazine, diuron, 3,4-dichlorophenylmethylurea, 3,4-dichlorophenylurea (DPU), monuron, bentazone, anthranil-isopropylamide, chloridazon, metolachl or] in surface, estuarine and sea water samples at the low ng/l level. Soli d-phase extraction is combined off-line with column liquid chromatography-e lectrospray ionization tandem mass spectrometric detection (LC-ESI-MS-MS). The applicability of two solid-phase materials, i.e., LiChrolut EN cartridg es and graphitized carbon black extraction disks, is evaluated. The influen ce of the organic solvent used in gradient LC, as well as the amount of co- extracted humic material on the ESI process is studied. The eluotropic stre ngth of the organic solvent was found to have a distinct effect on the sens itivity of ESI-MS if coupled with LC gradient separations. Methanol gave mu ch better results than acetonitrile and phenylurea compounds are more susce ptible to solvent changes than triazines. Go-extracted humic material cause s signal suppression in ESI-MS-MS detection. The degree of suppression depe nds upon the sample pH and the nature of the samples, i.e., surface or estu arine water. Detection limits in LC-ESI-MS-MS ranged from 0.2 to 2 ng/l, wi th the exception of DPU (8 ng/l). The applicability of the procedure was de monstrated by analyzing surface and estuarine water. (C) 1999 Elsevier Scie nce B.V. All rights reserved.