Automated sample clean-up procedure for organophosphorus pesticides in several aquatic organisms using normal phase liquid chromatography Original Research Article

Automated procedures based on normal phase liquid chromatography (LC) have been developed for the sample clean-up of phytoplankton, crustaceans and fish extracts prior to gas chromatographic analysis of organophosphorus pesticide residues (phorate, dimethoate, fonofos, fenitrothion, malathion, chlorpyrifos, chlorfenvinphos, methidathion and phosmet). Extraction was carried out by high speed blending with acetonitrile:acetone (90:10, v/v). The extract was concentrated by a Kuderna–Danish evaporation system and evaporated to dryness under a gentle stream of nitrogen at 40°C and the residue was dissolved in n-hexane. A 1 ml portion of the hexane extract was injected on the LC system using a silica-gel column and diode array detection for the on-line monitoring of lipid elution. Difference in behavior of lipids present in marine organism extracts and the wide polarity range of pesticides studied made necessary the design of specific elution procedures for each species in order to obtain pesticides in fat-free fractions using different mixtures of hexane–ethyl acetate as mobile phases. The automated sample clean-up procedures developed allowed the direct injection of 1 ml LC fractions containing pesticides in the gas chromatography (GC) system. Recoveries of pesticides in spiked samples after application of the overall procedure, including extraction of samples, LC automated clean-up and GC analysis, ranged from 80% to 114% (except for phorate, 68%) and limits of detection were found to be between 2 and 10 ng g−1 by using as little as 1 g of sample per analysis. The procedures developed offer several advantages: they are very efficient for fat elimination, the solvent consumption is low, and they allow fully automated clean-up. They were applied in bioaccumulation studies performed on molluscs, crustaceans and fish, and also to natural samples collected from different pollution vulnerable areas at the Mediterranean Spanish coast.