A simple method was proposed for simultaneous determination of chlorpyrifos and its hydrolysis and biodegradation product 3,5,6-trichloro-2-pyridinol (TCP) in soil samples. The analytes were extracted with ethyl acetate (EtOAc) under optimized pretreatment conditions such as the type, volume and pH of extraction solvent. Clean-up of the extract from soil was conducted by dispersive solid phase extraction (DSPE) using activated carbon as the adsorbent. High performance liquid chromatography with ultraviolet detection (HPLC-UV) was used for simultaneous determination of the two analytes. Under the optimized HPLC conditions, the limits of detection (LOD), obtained on signal-to-noise ratio (S/N) of 3, for chlorpyrifos and TCP were 0.0080 mg kg−1 and 0.0120 mg kg−1, respectively. Linear calibration curves were obtained in the range of 0.05–2.00 mg kg−1 and 0.03–2.00 mg kg−1 for chlorpyrifos and TCP, respectively. The spike recoveries from soil ranged from 89.4% to 114%, and the relative standard deviation (RSD) was in the range of 0.80%–14%.
