Improved determination of phoxim residue in stored wheat by HPLC with DAD

This article presents an improved method to detect the phoxim residual in whole wheat grain (not milled). The authors used petroleum ether (PE) as solvent to extract phoxim in darkness, and then determined it with high-performance liquid chromatography (HPLC) with diode array detector (DAD) at 280 nm. Use of PE improved the extraction efficiency of phoxim from grain samples over those obtained using acetone, recovery of 83.3% and 65.9%, respectively. Light produced more side effect on the extraction of this pesticide than with darkness, recovery of 63.2% and 83.3%, respectively. The combination of PE with darkness yielded a higher recovery of phoxim in liquid-phase extraction. The peak area of phoxim compared with its absolute values of phoxim in standard solution concentration range from 0.005 mg/kg to 0.253 mg/kg showed a good linear calibration (R(2) = 0.9999). Recoveries, at spiked concentrations of 0.02, 0.05, and 0.10 mg/kg, varied between 83.3% and 106.3% with relative standard deviations (RSD) ranging from 6.5% to 8.0%. The present method provides sufficient sensitivity as reflected by the values of limit of detection (LOD) and limit of quantification (LOQ). LOD was 0.002 mg/kg (S/N 3), and the estimated LOQ was 0.006 mg/kg (S/N = 10). Use of the proposed method successfully detected phoxim residue in wheat grain from Beijing and Kunming City of China.