Analysis of 17 polar to semi-polar pesticides in the Ebro river delta during the main growing season of rice by automated on-line solid-phase extraction-liquid chromatography–tandem mass spectrometry

This work describes the optimization of a fully automated method based on on-line solid-phase extraction-liquid chromatography–electrospray–tandem mass spectrometry (SPE-LC–ESI-MS/MS) for the simultaneous determination of 17 medium to polar pesticides in water. The list of target analytes included organophosphates, triazines, phenylureas, anilides, chloroacetanilides, acidic herbicides and thiocarbamates. Detection limits achieved were below 5 ng/L for all compounds except metolachlor (12 ng/L), alachlor (17 ng/L), malathion (36 ng/L) and fenitrothion (50 ng/L). The method developed was used to investigate the occurrence of the target pesticides in a total of 52 water samples collected monthly (from May to August 2005) at 14 selected locations in the rice cultivation area of the Ebro river delta. The study showed high levels, in the μg/L range, of bentazone, MCPA, propanil, molinate and atrazine, in basically all the samples investigated. The remaining pesticides were present at lower levels (<0.1 μg/L) or only detected sporadically (e.g. fenitrothion and malathion). The sampling campaign performed in July showed comparatively higher levels than the other three campaigns.