Highly selective sample preparation and gas chromatographic–mass spectrometric analysis of chlorpyrifos, diazinon and their major metabolites in sludge and sludge-fertilized agricultural soils

A pressurized liquid extraction (PLE) solid-phase extraction (SPE) gas chromatography–mass spectrometry (GC–MS) method was developed for the determination of two model organophosphorus pesticides (OPPs), i.e. chlorpyrifos (CPF, O,O-diethyl-O-[3,5,6-trichloro-2-pyridyl]-phosphorothioate, CAS no. 2921-88-2) and diazinon (DZN, O,O-diethyl-O-2-isopropyl-4-methyl-6-pyrimidyl thiophosphate, CAS no. 333-41-5) and their two more stable metabolites namely, 3,5,6-trichloro-2-pyridinol (TCP, CAS no. 6515-38-4) and 2-isopropyl-6-methyl-4-pyrimidinol (IMHP, CAS no. 28-14-20-2) in sewage sludge and agricultural soil samples was developed. A PLE procedure was optimized as a less time-consuming and cost-effective extraction approach for sewage sludge/soil samples. Derivatization of metabolites was carried out with N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide (MTBSTFA) to form stable derivatives. The method was developed using spiked soil samples at 1 mg/kg for the intact insecticides and at 2 mg/kg for their metabolites. Recovery yields for the target pesticides were > 92%, meanwhile for the metabolites the recoveries were somewhat low. Limits of quantification (LOQ) were within the range of 4–62 ng/g for the sludge sample and between 3 and 31 ng/g for sludge-fertilized soil samples. The method was applied for the determination of both insecticides in some soils fertilized with sludge from municipal wastewater treatment plants (WWTPs) in the proximity of Barcelona (Catalonia, Spain) and in one representative sludge sample used as fertilizer. Results revealed the presence of CPF in all samples at concentrations within the range of 210.32–38.36 ng/g. Both major metabolites were also found to be present in all samples.