Determination of metolcarb residue in rice and paddy field by ultra high performance liquid chromatography tandem mass spectrometry

An analytical method was established to determine metolcarb in paddy soil,paddy water,rice straw,rice hull and brown rice by ultra high performance liquid chromatography tandem mass spectrometry(UPLC-MS/MS).Metolcarb residues in rice samples were extracted by acetonitrile and subjected to a salting-out procedure.The samples were further purified by N-propyl-ethylenediamine(PSA) and white carbon black(SiO2·nH2O),then analyzed by UPLC-MS/MS in the mode of multiple reaction monitoring.The linearity was satisfactory in the concentration range of 0.005-1 mg/L, with a correlation coefficient r>0.98.When metolcarb was spiked at 0.01-5 mg/kg level in soil matrix and at 0.005-1 mg/L level in water matrix,the average recoveries of metolcarb in different matrices varied from 76.7% to 107.8%,the relative standard deviation (RSD) varied from 1.7% to 8.5% and the method limit of detection (LOD) was 2.0×10-13 g.Moreover,the limit of quantification (LOQ) in paddy soil,rice straw,rice hull and brown rice were 0.01 mg/kg and 0.005 mg/L in paddy water.The developed method was applied for terminal residue study.When metolcarb was applied for two and three times at the recommended dose of 1.5 times(45 g/hm2,a.i.),the finial residues in brown rice was not detected (lower than 0.01 mg/kg),at the sampling intervals of 10 d,14 d and 21 d after the last application.