Simple Solvent Extraction Coupled with Liquid Chromatography-High-Resolution Mass Spectrometry for the Analysis of Pesticide Residues in Rice Bran Protein Powder

Abstract

A simple analytical method combining solvent extraction and liquid chromatography-high-resolution mass spectrometry (LC-HRMS) was developed for the analysis of pesticide residues in rice bran protein powder. Owning to the high accuracy of HRMS in determination of mass to charge ratio (m/z), a suspect screen of pesticide residues was performed by LC-HRMS prior to quantification analysis. Based on the theoretical m/z, four pesticides including isoprothiolane (IPT), tebuconazole (TBZ), propiconazole (PCZ), and tricyclazole (TCZ) were detected and further verified with their reference standards. The solvent extraction conditions were optimized according to the signal intensity of extracted ion chromatogram (XIC) in LC-HRMS. After optimization, 50% acetonitrile solution was adopted, in which the targeted pesticides could be extracted effectively (recoveries/accuracy of > 85%) with the good reproducibility (relative standard deviation (RSD) < 10.3%). Two isotope internal standards isoprothiolane-D4 (IPT-D4) and propiconazole-D5 (PCZ-D5) were applied in quantification, and the quantification results were highly consistent with those from the standard addition method. Limit of detections (LODs) and limit of quantifications (LOQs) of the method were about 0.05–0.2 and 0.2 to 1 μg kg−1, respectively, without additional purification/enrichment for these analytical targets. The developed method was applied for the analysis of five different batches of rice bran protein samples. It was found that these four pesticide residues were all below 0.02 mg kg−1, well less than the maximum residue levels (MRLs) in the latest regulations in EU and China (0.1–5 mg kg−1). Besides the rice bran protein powder, this suspect screen followed with targeted quantification approach by LC-HRMS could also be applied for other rice derivative products analysis.