AUTOMATED SAMPLE CLEANUP AND FRACTIONATION OF CHLORPYRIFOS, CHLORPYRIFOS-METHYL AND METABOLITES IN MUSSELS USING NORMAL-PHASE LIQUID-CHROMATOGRAPHY

An automated method based on normal-phase LC has been developed for th e sample clean-up of mussel extracts prior to gas chromatographic anal ysis of residues of chlorpyrifos, chlorpyrifos-methyl and their metabo lites chlorpyrifos-methyl-oxon and 3,5,6-trichloro-2-pyridinol. Pestic ides were extracted by means of a high speed blender using acetonitril e-acetone (90:10, v/v). The extract obtained was filtered and concentr ated using rotavapor and the residue was dissolved in hexane. One mi o f the hexanoic extract was injected on the silica-gel column, using he xane as mobile phase. Pesticides and metabolites were eluted in fat-fr ee fractions with different mixtures of hexane-ethyl acetate. Diode ar ray detection allowed monitoring on-line the elution of lipids. Purifi ed extracts were analyzed by GC using nitrogen-phosphorus detection fo r quantitation and MS for confirmatory purposes, The method is fully a utomated from the injection of the extract to the collection of fracti ons, which are directly injected into the GC system. In this way, neit her further clean-up nor solvent exchange were necessary prior to GC a nalysis. Recoveries obtained from fortified mussel samples at two conc entration levels -100 and 20 ng g(-1) for parent pesticides and 200 an d 40 ng g(-1) for metabolites- were higher than 90%. Limits of detecti on of the whole procedure of analysis were lower than 1 ng g(-1) for p arent pesticides and than 10 ng g(-1) for metabolites, This method has been successfully applied to bioconcentration studies with mussels ex posed to chlorpyrifos. Chlorpyrifos and its metabolic derivative 3,5,6 -trichloro-2-pyridinol were detected and confirmed by MS in analyzed s amples. (C) 1997 Elsevier Science B.V.