LARGE-VOLUME INJECTION IN GAS CHROMATOGRAPHYN ION-TRAP TANDEM MASS-SPECTROMETRY FOR THE DETERMINATION OF PESTICIDES IN THE MARINE-ENVIRONMENT AT THE LOW NG L LEVEL/

Analytical procedures are developed for the identification and quantif ication of pesticides in the marine environment. Concentrations in the marine environment are expected to be at or below the low ng/l level, which requires preconcentration of analytes and improved detection. O ff-line solid phase extraction (SPE) was combined with large-volume in jection gas chromatography (GC) by means of a programmable temperature vaporiser (PTV). The selectivity of the detection procedure was consi derably increased by using tandem mass spectrometry (MS/MS) instead of single-MS operation. Two ionisation modes, i.e. electron impact (EI) and positive chemical ionisation (PCI) with acetonitrile as reagent ga s, were studied for the determination of five test analytes, i.e. atra zine, desethylatrazine, simazine, alachlor and metolachlor. The detect ion Limits for both ionisation modes were essentially the same, and ra nged between 0.2 and 5 ng l(-1) when using a sample volume of 200 ml. With this modest sample volume, simultaneous filtration and extraction of even low-salinity samples could be performed without the filter be ing blocked by the large amount of suspended matter present in such sa mples. (C) 1997 Elsevier Science B.V.