Large-volume injection in gas chromatography-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 quantification 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. Off-line solid phase extraction (SPE) was combined with large-volume injection gas chromatography (GC) by means of a programmable temperature vaporiser (PTV). The selectivity of the detection procedure was considerably 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 gas, were studied for the determination of five test analytes, i.e. atrazine, desethylatrazine, simazine, alachlor and metolachlor. The detection limits for both ionisation modes were essentially the same, and ranged 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 being blocked by the large amount of suspended matter present in such samples.