Parameters affecting microwave-assisted extraction of organophosphorus pesticides from agricultural soil

• Published in: Journal of Chromatography A 2007-10, Vol.1169 (1), p.40-46
• Main Authors: Fuentes, Edwar, Báez, María E., Labra, Ronnie
• Format: Article
• Language: English
• Subjects: agricultural soils; Agriculture; Analysis methods; Analytical chemistry; Applied sciences; Chemical Fractionation - methods; Chemistry; Chemometric approach; Chile; Chromatographic methods and physical methods associated with chromatography; Chromatography, Gas - methods; Diazinon; ethoprophos; Exact sciences and technology; extraction; Fenitrothion; flame photometric detection; Gas chromatographic methods; gas chromatography; GC–FPD; Hexanes - chemistry; insecticide residues; KH 2PO 4 effect; Methyl Parathion; methyl pirimiphos; microwave treatment; Microwave-assisted extraction; Microwaves; Organophosphorus Compounds - isolation & purification; organophosphorus insecticides; Organophosphorus pesticides; Organothiophosphorus Compounds; parathion; parathion-methyl; pesticide residues; Pesticide Residues - isolation & purification; Phosphates - chemistry; Photometry - methods; Pollution; Potassium Compounds - chemistry; Sensitivity and Specificity; Soil - analysis; Soil and sediments pollution; Soil Pollutants - chemistry; Soil Pollutants - isolation & purification; soil pollution; Soils
• ISSN: 0021-9673
• DOI: 10.1016/j.chroma.2007.08.064

This work describes an optimised method for the determination of six representative organophosphorus pesticides (OPPs) (diazinon, parathion, methyl pirimiphos, methyl parathion, ethoprophos, and fenitrothion) in agricultural soils. The method is based on microwave-assisted extraction using a water–methanol modified mixture for desorption and simultaneous partitioning on n-hexane (MAEP), together with gas chromatography–flame photometric detection (GC–FPD). To improve GC–FPD signals (peak intensity and shape) olive oil was used effectively as a “matrix mimic”. The optimisation of the extraction method was achieved in two steps: an initial approach through experimental design and principal component analysis where recovery of compounds using a water–methanol mixture ranged from 54 to 77%, and the second one by studying the addition of KH 2PO 4 to the extracting solution where recoveries were significantly increased, molecular replacing of OPPs from adsorption sites by phosphate being the probable extraction mechanism. Under optimised conditions, recoveries of pesticides from different soils were higher than 73%, except for methyl parathion in some soils, with SD equal or lower than 11% and detection limits ranging from 0.004 to 0.012 μg g −1. The proposed method was used to determine OPPs in soil samples from different agricultural zones of Chile.