Determination of the residues of three pesticides and two metabolites in rice by ultra-high performance liquid chromatography-tandem mass spectrometry

An analytical method based on ultra-high performance liquid chromatography-tandem mass spectrometry was established and optimized for simultaneous determination of emamectin benzoate, chlorantraniliprole, fluxapyroxad and its metabolites M700F008 and M700F048 in rice. Rice husk and brown rice were extracted with 0.2% formic acid-acetonitrile and cleaned up with C₁₈, while rice straw was extracted with 1% formic acid-acetonitrile and cleaned up with N-propyl ethylenediamine (PSA) and graphitized carbon black (GCB). T3 chromatographic column was used for separation and the mobile phase was methanol and 0.2% formic acid water. Electrospray ionization in positive ion mode was selected, the detection mode was multi-reaction monitoring, and external standard method was used for quantification. The results showed that there was a good linear relationship between the mass concentration and peak area of the five tested compounds, and the determination coefficient was greater than 0.9955. The average recoveries of the five compounds in rice husk, brown rice and rice straw were in range of 71%-119% with the relative standard deviations (RSD) of 1%-11%, which met the requirements of residue analysis. The residues of emamectin benzoate, chlorantraniliprole and fluxapyroxad in brown rice samples collected from three locations were all lower than MRLs in China.