Determination of organophosphorus pesticides using membrane-assisted solvent extraction combined with large volume injection-gas chromatography-mass spectrometric detection.

Eight organophosphorus pesticides (parathion-methyl, fenitrothion, malathion, fenthion, bromophos, bromophos-ethyl, fenamiphos and ethion) in aqueous samples were analysed by means of membrane-assisted solvent extraction. First a 20 ml extraction vial was filled with 15 ml of aqueous sample. Then the membrane bag consisting of nonporous polypropylene was put into the vial and filled with 800 microl of organic solvent. The analytes were separated from the aqueous layer by transporting them through the membrane material into the small amount of solvent. The technique was fully automated and successfully combinable with large volume extraction and GC-MS. To achieve an optimum performance several extraction conditions were investigated. Cyclohexane was chosen as acceptor phase. Then the impact of salt, methanol, pH value, as well as working parameters like stirring rate of the agitator and extraction time, were studied. Moreover, the influence of matrix effects was examined by adding different concentrations of humic acid sodium salt. Detection limits in the ng/l level were achieved using large volume injection with the injecting volume of 100 microl. The recovery values ranged from 47 to 100% and the relative standard deviation for three standard measurements was between 4 and 12% (except for bromophos-ethyl: 22%). The linear dynamic range was between 0.001 and 70 microg/l. The applicability of the method to real samples was tested by spiking the eight organophosphorus pesticides to red wine, white wine and apple juice samples.