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A method for analysis of 37 pesticide residues in tea samples was developed and validated and was based on reversed-dispersive solid-phase extraction (r-DSPE) cleanup in acetonitrile solution, followed by liquid chromatography–electrospray tandem mass spectrometry determination. Green tea, oolong tea, and puer tea were selected as matrixes and represent the majority of tea types. Acetonitrile was used as the extraction solvent, with sodium chloride and magnesium sulfate enhancing partitioning of analytes into the organic phase. The extract was then cleaned up by r-DSPE using a mixture of multiwalled carbon nanotubes, primary secondary amine, and graphitized carbon black as sorbents to absorb interferences. Further optimization of sample preparation and determination allowed recoveries of between 70% and 111% for all 37 pesticides with relative standard deviations lower than 14% at two concentration levels of 10 and 100 μg kg–1. Limits of quantification ranged from 5 to 20 μg kg–1 for all pesticides. The developed method was successfully applied to the determination of pesticide residues in market tea samples.

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A modified QuEChERS and LC-MS/MS method has been developed for the simultaneous determination of residues of six neonicotinoids in various crops, including spinach, cucumber, apple and pomelo. The method showed good linearity (R(2) ≥ 0.9995) and precision (RSD ≤ 14.0%). Average recoveries of the six neonicotinoids ranged between 73.7% and 103.8% at spiking levels 0.005, 0.1 and 1 mg kg(-1). The LODs and LOQs were in the ranges of 0.20-0.85 μg kg(-1) and 0.66-2.84 μg kg(-1), respectively. The method was satisfactorily validated for the analysis of 50 agricultural samples. Imidacloprid and imidaclothiz were detected at concentration levels ranging from 7 to 5.3 μg kg(-1).

To select representative leaf vegetables which may contain the highest residue, field experiments of metalaxyl, fluazifop-P-butyl, chlorpyrifos, and lambda-cyhalothrin on six crops including pakchoi, rape, crown daisy, amaranth, spinach, and lettuce were designed and conducted. In this study, a high-performance liquid chromatograph and electrospray ionization tandem mass spectrometer with multiple reaction monitoring was used to simultaneously determine metalaxyl and fluazifop-P-butyl residue in various samples, and a gas chromatograph with electron capture detector was used to detect chlorpyrifos and lambda-cyhalothrin. The limits of quantification (LOQ) of metalaxyl, fluazifop-P-butyl, chlorpyrifos, and lambda-cyhalothrin were in the range of 0.001-0.01 mg kg(-1) for all samples, and the average recoveries of all pesticides ranged from 67.6 to 119.1% at spiked levels of 0.01-0.1 mg kg(-1). In supervised field trials, the half-lives of metalaxyl, fluazifop-P-butyl, chlorpyrifos, and lambda-cyhalothrin were in the range of 1.11-3.79 days, 1.11-2.27 days, 1.13-5.17 days, and 1.77-6.24 days. It was also found that all pesticide residues in spinach and/or amaranth were higher than others after application. It is recommended that spinach or amaranth can be selected as a representative crop of leaf vegetables in studying systemic fungicide, insecticides, and herbicides with similarity as metalaxyl, fluazifop-P-butyl, chlorpyrifos, and lambda-cyhalothrin.

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RATIONALE Direct analysis in real time (DART) is a new ion source technique, which is conducted in the open air under ambient conditions, applied to the rapid and direct analysis of any material (gases, liquids, and solids) with minimal or no sample preparation. In order to take advantage of the capacity of DART mass spectrometry for the real‐time analysis of hazardous ingredients in commercial agrochemicals, a pilot study of rapid qualitative determination of hazardous pesticides was performed. METHODS Highly hazardous pesticides were identified by DART ionization coupled to a single‐quadrupole mass spectrometer (DART‐MS). Acetonitrile was chosen for dissolving samples prior to the analysis. Samples were analyzed by this technique in as little as 5 s. RESULTS Phorate, carbofuran, ethoprophos and fipronil were be detected directly from commercial agrochemicals. The ionization‐related parameters (DART temperature, grid voltage and MS fragment) of these compounds were optimized to obtain highly response. Isotope patterns were taken into consideration for qualitative identification. Relative standard deviations (RSDs, n = 5) of 2.3–15.0% were obtained by measuring the relative abundance of selected isotopes. CONCLUSIONS This study showed that DART‐MS technology was able to qualitatively determine the existence of highly hazardous pesticides in commercial pesticide formulations. It is suggested that this technology should be applied for routine monitoring in the market. Copyright © 2012 John Wiley & Sons, Ltd.