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3.Determination of dimethoate and fenitrothion in estuarine samples by C-18 solid-phase extraction and high-resolution gas-chromatography with nitrogen-phosphorus detection V. K. Karamfilovb, a, T. W. Filemanb, K. M. Evansb and R. F. C. MantouraAnalytica Chimica Acta Volume 335, Issues 1-2, 10 December 1996, Pages 51-61 AbstractDimethoate [S-((2-(methylamino)ethyl)-2-oxoethyl)phosphorodithioate] and fenitrothion [O,O-dimethyl O-(4-nitro-m-tolyl)phosphorothioate], both organophosphorus pesticides (OPs), have been successfully enriched on monofunctional C-18 solid-phase extraction (SPE) cartridges and quantified by high-resolution capillary gas-chromatography with nitrogen-phosphorus detection (GC-NPD). The method was optimised for estuarine conditions. The recoveries varied significantly with the pH values of spiked seawater samples in the range pH 6.5–9.0 for both compounds. Salinity did not affect the recoveries of fenitrothion whereas the recoveries of dimethoate increased with salinity. The highest recoveries from water samples spiked at trace concentrations of 100 ng l?1 were 68% and 91% for dimethoate and fenitrothion, respectively, and were achieved at pH 6.5 and a salinity of 36‰. Recoveries from ultrasonically extracted sediments, spiked at 100 ng g?1 dry weight were 91% for dimethoate and 86% for fenitrothion. The detection limits (s/n = 3) for dimethoate and fenitrothion in water and sediment samples were 1 ng l?1 and 2 ng g?1 dry weight, respectively. The reproducibility (RSD) of all determinations was 10%. Comparison of the GC-EI-MS spectra showed that ions m/z 87,93 and 229 for dimethoate and m/z 109, 260 277 for fenitrothion are suitable for selective ion monitoring. The method was not suitable for extraction and quantification of dimethoxon, an oxygen analogue of dimethoate, as the recoveries were always below 20%. GC column lifetime was significantly improved after calibrations were performed with standard solutions prepared in OP-free extracts of natural samples.4.Comparison of Soxhlet and Microwave-Assisted Extractions for the Determination of Fenitrothion Residues in Beans Rokhaya G. Diagne, Gregory D. Foster, and Shahamat U. KhanJ. Agric. Food Chem., 50 (11), 3204 -3207Abstract:White and black "niebe" beans [Vigna unguiculata (L.) Walp] from Senegal were treated with fenitrothion (O,O-dimethyl O-4-nitro-m-tolyl phosphorothioate), and the residues were determined by high-performance liquid chromatography (HPLC) and electron capture gas chromatography (EC-GC). Fenitrothion residues from the beans were extracted by Soxhlet extraction (SE) and microwave-assisted extraction (MAE). A column cleanup procedure was used to remove the coextractives in the extract before HPLC and EC-GC analyses. The overall mean recoveries of fenitrothion residues in the 0.19-1.90 g/kg fortification range determined from extracts obtained by SE and MAE were 88.4 and 89.8%, respectively, with respective relative standard deviations of 4%. The results show that MAE is a viable alternative to the commonly used SE for the determination of fenitrothion residues in beans.

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