AbstractThe solid‐phase microextraction (SPME) technique using a 100 μm film poly(dimethylsiloxane) (PDMS) has been examined with the aim to determine butachlor in aqueous samples. The feasibility of SPME gas chromatography‐electron capture detection (GC‐ECD) analysis has been evaluated. From this study the equilibrium distribution constant between PDMS coating and water for butachlor obtained was 1.9 × 103with a 5.3% RSD. Extraction time of 40 min, desorption time of 3 min and desorption temperature of 250 °C were selected. The effect of salt addition was examined. The inhibitions of methanol and humic acid to the extraction of butachlor were observed. A standard addition method for calibration was recommended to reduce the deviation from matrix interference. Linear ranges from 0.1 to 12 μg/L and limits of detection of 0.007 μg/L for deionized water, 0.010 μg/L for ground water, and 0.016 μg/L for irrigated water were obtained. The proposed method was applied to determine butachlor in irrigated water. The degradation of butachlor in aqueous solution under the irradiation of 253.7 nm light has been measured by the developed SPME‐GC‐ECD procedure. The half‐life of the aqueous butachlor fou