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In this study, headspace solid phase microextraction (HS-SPME) followed by gas chromatography using electron capture detection system (GC-ECD) were developed for the determination of chloraacetanilide (butachlor) and chlorpyrifos presented in biological samples. Different parameters affecting the extraction procedure were optimized including extraction time (30 minutes), extraction temperature (80˚C), sample volume (3 mL), sample pH (2), added NaCl (0.3 gram) and sample stirring rate (400 rpm). Different concentrations of 1 -100 ng/ml were applied for butachlor and a linear calibration curve was obtained. Furthermore, a similar linearity was obtained for chlorpyrifos, using a concentration range of 1 -250 ng/ml. The limit of detection (LOD) obtained for butachlor and chlorpyrifos were 0.088 and 0.53 ng/ml respectively. The optimized methods for both compounds were validated using two concentrations of 25 and 50 ng/ml in spiked urine samples. Obtained recoveries of spiked urine samples were 83.06% -99.8% with RSD of lower than 11%. Optimized technique was simple, inexpensive, solvent free and fast in comparison with other conventional methods and had compatibility with the chromatographic analytical system. This method offers low detection limits to analyze pesticides in urine samples that are very important * Corresponding author. F. Ghavidel et al. 536in the exposure monitoring in occupational health.

Microwave assisted head-space solid phase microextraction (MA-HS-SPME) followed by gas chromatography using electron capture detection system (GC-ECD) were developed for determination of chloraacetanilide (butachlor) and chlorpyrifos present in biological samples. The different parameters including microwave irradiation power and microwave irradiation time, which affected on the extraction rate, were optimized. The optimum conditions for extraction of both pesticides were as following: irradiation power of 600 W, microwave irradiation time 10 min, sample volume: 10 ml, sample pH=2 and added salt 10 %. The limit of detection (LOD) for butachlor and chlorpyrifos were 0.0864 and 0.0832 ng/ml, respectively. The optimized methods for both compounds were validated for 6 consequtive days and 6 inter-day using two concentrations of 10 and 100 ng/ml in spiked urine samples that the ranges of obtained recoveries were 91-104 %.

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