title: Parameters affecting microwave-assisted extraction of organophosphorus pesticides from agricultural soil.
abstract: 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 KH2PO4 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 microg g(-1). The proposed method was used to determine OPPs in soil samples from different agricultural zones of Chile.
authors.affiliation: Departamento de Química Inorgánica y Analítica, Facultad de Ciencias Químicas y Farmacéuticas, Universidad de Chile, Santiago, Casilla 233, Chile. edfuentes@ciq.uchile.cl
authors.forename: Edwar
authors.initials: E
authors.lastname: Fuentes
authors.forename: María E
authors.initials: ME
authors.lastname: Báez
authors.forename: Ronnie
authors.initials: R
authors.lastname: Labra
mesh_terms: D000383:Agriculture; D005591:Chemical Fractionation / Q000379:methods; D002677:Chile; D002849:Chromatography, Gas / Q000379:methods; D003976:Diazinon; D005278:Fenitrothion; D006586:Hexanes / Q000737:chemistry; D008743:Methyl Parathion; D008872:Microwaves; D009943:Organophosphorus Compounds / Q000302:isolation & purification*; D063086:Organothiophosphates; D009946:Organothiophosphorus Compounds; D010573:Pesticide Residues / Q000302:isolation & purification*; D010710:Phosphates / Q000737:chemistry; D010783:Photometry / Q000379:methods; D017680:Potassium Compounds / Q000737:chemistry; D012680:Sensitivity and Specificity; D012987:Soil / Q000032:analysis*; D012989:Soil Pollutants / Q000737:chemistry / Q000302:isolation & purification*
chemical_list: D006586:Hexanes; D009943:Organophosphorus Compounds; D063086:Organothiophosphates; D009946:Organothiophosphorus Compounds; D010573:Pesticide Residues; D010710:Phosphates; D017680:Potassium Compounds; D012987:Soil; D012989:Soil Pollutants; C001182:ethoprop; C026385:n-hexane; D008743:Methyl Parathion; C013216:potassium phosphate; D005278:Fenitrothion; D003976:Diazinon