Residue of pyriminobac-methyl in rice and environment

A method was developed for the determination of pyriminobac-methyl residues in rice and environment by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS) coupled with modified QuEChERS. The samples were extracted with a solvent mixture, V (acetonitrile) : V (formic acid) = 199 : 1, and then purified by octadecylsilane bonded silica (C₁₈) or C₁₈ + primary secondary amine (PSA) adsorbents. The analytes were separated on a ZORBAX SB C₁₈ column using a solvent mixture, V (acetonitrile) : V (0.1% formic acid aqueous solution) = 70 : 30, as mobile phase. Pyriminobac-methyl was detected by HPLC-MS with an electrospray ionization source (ESI⁺) in positive mode. Quantization was performed using external standard method. The results showed good linear relationship between the peak area of pyriminobac-methyl and its mass concentration in the range from 0.01 mg/L to 1 mg/L. And the correlation coefficients in acetonitrile, paddy water, soil, rice stalk, brown rice and rice husk were all above 0.99. The limit of detection (LOD) for pyriminobac-methyl was 0.0015 mg/L in paddy water, while the limit of quantification (LOQ) was 0.005 mg/L. The LOD were 0.003, 0.015, 0.015 and 0.003 mg/kg in soil, brown rice, rice hull and rice stalk, respectively, while the corresponding LOQ were 0.01, 0.05, 0.05 and 0.01 mg/kg, respectively. The average spiked recoveries of pyriminobac-methyl at three spiked levels of 0.005, 0.01 and 0.1 mg/L (or mg/kg) in paddy water, soil and brown rice were 95%-109%, 92%-106% and 89%-107%, respectively, with the relative standard deviation (RSD) of 3.0%-5.0%, 1.1%-2.9% and 3.1%-3.7%, respectively. The average spiked recoveries in rice hull and rice stalk were 95%-102% and 93%-107%, respectively, with the RSD of 1.1%-3.8% and 3.5%-9.9%, respectively. The sensitivity, precision and accuracy of the method meet the requirements of pesticide residue analysis.