Simultaneous determination of thiram and metalaxyl residues in rice and soil by dispersive solid phase extraction and high performance liquid chromatography-tandem mass spectrometry

A rapid analytical method for the simultaneous determination of thiram and metalaxyl in paddy soil, rice plant, rice husk and brown rice was developed using dispersive solid phase extraction and high performance liquid chromatography-tandem mass spectrometry(HPLC-MS/MS). The analytes was extracted by acetonitrile and cleaned up by PSA and C18, and then separated on a reversed phase C18 column using an isocratic elution program of 0.2% aqueous formic acid and acetonitrile. Qualitative analysis was performed with electrospray ionization in positive mode(ESI+) under multiple reaction monitoring(MRM) mode. Matrix-matched calibrations were respectively used to quantify the residue concentrations. In the concentration range of 1-500 μg/L, the matrix-matched calibration curves showed good linearity with correlation coefficients >0.991. Intra-day mean recoveries of thiram and metalaxyl in different matrices were found between 76% and 104% at 0.01-1.5 mg/kg, with relative standard deviations(RSD) of 1.2%-13.2%(n=5). Inter-day mean recoveries of thiram and metalaxyl were found between 74% and 102% with RSD of 2.8%-10.4% at 0.01-1.5 mg/kg(n=5). The method is simple, rapid, sensitive and accurate, which can meet the detection requirements of thiram and metalaxyl residues in rice samples and soil.