No abstract

An efficient and modified Quick Easy Cheap Effective Rugged and Safe (QuEChERS) method combined with liquid chromatography-electrospray ionization with tandem mass spectrometric detection were evaluated for the analysis of residues of 72 pesticides in brown rice including acidic sulfonylurea herbicides. For extraction of pesticides and clean-up of the extract, 1% formic acid in acetonitrile and dispersive solid phase extraction were used, respectively. Two fortified spikes at 50 and 200 µg L -1 levels were performed for recovery test. Mean recoveries of majority of pesticides at two spike levels ranged from 90 to 110% with standard error (Coefficient of Variation) less than 10%. The limits of detection and quantification ranged from 0.24 to 19.92 µg L -1 and 0.79 to 65.74 µg L -1 , respectively. Good linearity of calibration curves were achieved with R 2 > 0.9943 within the observed concentration range (from 20 to 400 µg L -1 ). The modified method also provided satisfactory results for sulfonylurea herbicides, which could not be determined properly with previously reported methods. This method was applied to determine residues of target pesticides in real samples. A total of 22 pesticides in 31 out of 40 tested samples were observed. The highest concentration was observed for tricyclazole at 1.17 mg L -1 . This pesticide found in two brown rice samples exceeded its MRL regulated for rice in Republic of Korea. Except this pesticide, concentrations of all observed pesticides were lower than their MRLs. The results reveal that the method is applicable for routine analysis of residues of target pesticides in brown rice.

In this article matrix components in spinach were investigated in detail. The samples were prepared using two QuEChERS (quick, easy, cheap, effective, rugged and safe) methods, AOAC and CEN. Liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS), gas chromatography-mass spectrometry (GC-MS) and ultra performance liquid chromatography-diode array detector (UPLC-DAD), were applied for component identification. The strategies of identification by LC-ESI-MS/MS include accurate mass spectra of the parent ion, comparison with previous literature data and investigation of the mass spectral decomposition pattern. Overall, fourteen components were identified by LC-ESI-MS/MS in each methods of AOAC and CEN, which were phytosteroids, flavonoids, fatty acids and fatty acid amides. Fifty components using AOAC method and fifty-seven components using CEN method were identified in GC-MS by comparing mass data with the National Institute of Standards and Technology (NIST, U.S.) database. The results indicate that the major components of the matrix are terpenoids, fatty acids and fatty acid esters. Moreover, three pigments (neoxanthin, violaxanthin and lutein) in the AOAC method and eight pigments (neoxanthin, violaxanthin, zeaxanthin, lutein, chlorophyll chlorophyll, pheophytin and beta-carotene) in the CEN method that gave a characteristics peak at 440 nm were identified by the UPLC-DAD. According to the sample preparation condition using different amounts of graphitized carbon black (GCB) in this study, the AOAC method had higher matrix component removal efficiency than the CEN method. A better understanding of matrix components would increase the current knowledge for improvement of existing QuEChERS methodology, as well as contribute to new method developments.