Solid phase microextraction of residues of organophosphorus pesticides from aqueous samples for their determination by gas chromatography-mass spectrometry

2993-2999While studying the individual parameters on the extraction efficacy of organophosphorus pesticides (OPPs) in aqueous samples by solid phase microextraction, the nature of fibre, equilibration time and the presence of salt (sodium chloride used) show significant influence on the process. Polyacrylate (PA) fibre, (85μm), has been found to be considerably more effective than polydimethylsiloxane (PDMS), not only in the optimum recovery but also in the extraction of all eleven tested OPPs as compared to six by 100 μ m PDMS and two by 7 μm PDMS. Optimum equilibration is reached in 60 min at 26°C with PA fibre. Salt concentration significantly decreases the extraction while other parameters such as desorption time (5 min or longer) and sample pH (5-7.5) do not have any influence. GC-MS has been carried out in the scan mode (m/z 45-450) and quantitation by selected ion extraction. Rectilinear calibration graph is obtained in the range 0.05-50 μg l-1 OPPs, the correlation coefficient (r) being between 0.9982 and 0.9999. The RSD in the analysis of 2 μg l-1 OPPs ranges from 2.5 to 4.6%, and the limit of detection is found to be 14-62 ng l-1. The method could be used for the analysis of OPPs in natural aqueous samples; one example of its application to vegetable extract has been demonstrated