Abstract: A method was developed for the rapid determination of residues of two pesticides (chlorpyrifos and carbosulfan) and toxic metabolites (carbofuran, 3-hydroxycarbofuran and 3,5,6-trichloro-2-pyridinol (3,5,6-TCP)) in polished rice by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The five analytes were extracted from samples with acidified acetonitrile, purified by solid phase extraction using C18 and primary secondary amine (PSA) sorbents, and separated on an Eclipse XDB-C18 column with gradient elution using a mobile phase composed of a mixture of methanol and 5 mmol/L ammonium formate aqueous solution containing 0.1% (V/V) formic acid. The qualitative analysis was conducted in?the?positive?and?negative?ionization?switching mode using multiple reaction monitoring (MRM). The quick, easy, cheap, effective, rugged, and safe (QuEChERS) method was optimized by comparing the extraction efficiencies of different concentrations of formic acid in order to improve the sensitivity of the method. The correlation coefficients (r) of the calibration curves for all analytes were above 0.998 in the concentration range from 0.2 to 1 000.0 μg/L. The limits of detection (LODs) and quantification (LOQs) of the method ranged from 0.3 to 1.7 μg/kg and from 1.0 to 5.0 μg/kg, respectively. The recoveries from blank samples spiked at three concentration levels (1, 10 and 100 μg/kg for chlorpyrifos, carbosulfan, carbofuran and 3-hydroxycarbofuran as well as 5, 25 and 125 μg/kg for 3,5,6-TCP) ranged from 72.0% to 99.6% with relative standard deviations (RSDs) from 0.6% to 12% (n = 6). The results show that the method is rapid and efficient, and is suitable for rapid determination of chlorpyrifos, carbosulfan and their metabolites in polished rice samples.

Key words: high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), QuEChERS, pesticides, metabolites, rice