Yuhong Qin

The comparison of dispersive solid phase extraction and multi-plug filtration cleanup method based on multi-walled carbon nanotubes for pesticides multi-residue analysis by liquid chromatography tandem mass spectrometry

In this study, dispersive-Solid Phase Extraction (d-SPE) cleanup and multi-plug filtration cleanup (m-PFC) methods were compared for 25 representative pesticides in six matrices (wheat, spinach, carrot, apple, citrus and peanut) by QuEChERS-LC-ESI-MS/MS detection. The type of sorbents in dispersive-SPE (d-SPE) was optimized for the above matrices. Multi-walled carbon nanotubes (MWCNTs), which mixed other materials like PSA (Primary Secondary Amines), GCB (Graphitized Carbon Black) and C18 (Octadecyl-silica), showed brilliant cleanup performance in multi residue monitoring (MRM) pesticide residue analysis. Cleanup effects with d-SPE and m-PFC methods were examined. When spiked at 3 concentration levels of 10, 100, 500 μg/kg in above matrices, for both d-SPE and m-PFC methods, the recoveries ranged from 70 to 110% with relative standard deviations (RSDs) lower than 20%. Limits of quantification (LOQs) for both cleanup methods ranged from 1 to 25 μg/kg. Matrix-matched calibrations were performed with the coefficients of determination more than 0.99 between concentration levels of 10-1000 μg/kg. It was found that m-PFC was more convenient and effective than d-SPE with the same sorbents, due to the increased contact time and contact area between the extracts and compressed sorbents. The study demonstrated that m-PFC method could be used as a rapid, convenient and high-throughput cleanup method for analysis of pesticide residues.

Simultaneous determination of 70 pesticide residues in leek, leaf lettuce and garland chrysanthemum using modified QuEChERS method with multi-walled carbon nanotubes as reversed-dispersive solid-phase extraction materials.

Leek, leaf lettuce and garland chrysanthemum are troublesome vegetables containing large amount of pigments which may bring serious matrix interferences in mass spectrometry analysis. Multi-walled carbon nanotubes (MWCNTs) have a good effect for the cleanup of troublesome matrix. So the study was designed to develop a multi-residue method for the determination of 70 pesticide residues in leek, leaf lettuce and garland chrysanthemum based on a modified QuEChERS procedure using MWCNTs as reversed-dispersive solid phase extraction (r-DSPE) materials to remove the interferences of pigments. PSA and GCB were used as comparison. LC-MS/MS was used to identify and quantify the residue levels of multi-pesticides. The clean-up performance of MWCNTs was demonstrated to be obviously superior to GCB and PSA. This method was validated on leek, leaf lettuce and garland chrysanthemum spiked at the concentration of 10, 50 and 100μgkg(-1) with five replicates. The recoveries of 70 pesticides ranged from 74% to 119%, with relative standard deviations (RSDs) lower than 14.2%. Good linearity (R(2)≥0.9903) was obtained at the range of 10-1000μg/L for all pesticides in the selected matrices. The limit of quantification (LOQs) and limit of detection (LODs) of the 70 pesticides for the selected matrices ranged from 0.3 to 7.9μgkg(-1) and from 0.1 to 2.4μgkg(-1) respectively. The method was successfully applied to the routine monitoring of pesticide residues in market samples.

Residue determination of glufosinate in plant origin foods using modified Quick Polar Pesticides (QuPPe) method and liquid chromatography coupled with tandem mass spectrometry

A sensitive and specific method for the determination of glufosinate in plant origin foods was developed. The method involves extraction using modified QuPPe method, clean-up by multi-walled carbon nanotubes (MWCNTs), derivatization with 9-fluorenylmethyl chloroformate (FMOC-Cl) and detection with liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). The method was validated on twelve matrices spiked at 10 or 20, 100 and 500 μg/kg. The recovery ranged from 80% to 108% with intra-day RSDs (n=5) of 0.6-9.8% and inter-day RSDs (n=15) of 3.0-9.4%. Good linearities (R(2)⩾0.9991) were obtained for all matrices. The limit of detection (LOD) and limit of quantification (LOQ) for the selected matrices ranged from 0.3 to 3.3 μg kg(-1) and from 1 to 10 μg kg(-1), respectively. The method was demonstrated to be reliable and sensitive for the routine monitoring of glufosinate in plant origin foods.

Multi-residue determination of 171 pesticides in cowpea using modified QuEChERS method with multi-walled carbon nanotubes as reversed-dispersive solid-phase extraction materials

A rapid and sensitive method for the determination of 171 pesticides in cowpea was developed using multi-walled carbon nanotubes (MWCNTs) as reversed-dispersive solid-phase (r-DSPE) extraction materials. The clean-up performance of MWCNTs was proved to be obviously superior to PSA and GCB. This method was validated on cowpea spiked at 0.01 and 0.1mgkg(-1) with five replicates. The mean recoveries for 169 pesticides ranged from 74% to 129% with relative standard deviations (RSDs) (n=5) lower than 16.4%, except diflufenican and quizalofop-ethyl. Good linearity for all pesticides was obtained with the calibration curve coefficients (R(2)) larger than 0.9970. The limit of detection (LODs) and limit of quantification (LOQs) for the 171 pesticides ranged from 0.001 to 0.003mgkg(-1) and from 0.002 to 0.009mgkg(-1), respectively. The method was demonstrated to be reliable and sensitive for the routine monitoring of the 171 pesticides in cowpea samples.

Analytical method for 44 pesticide residues in spinach using multi‐plug‐filtration cleanup based on multiwalled carbon nanotubes with liquid chromatography and tandem mass spectrometry detection

Spinach is one of the most commonly planted vegetables worldwide. A high chlorophyll content makes spinach a complicated matrix in pesticide residue analysis. In this study, a rapid clean-up method was developed for the analysis of pesticide multi-residues in spinach followed by liquid chromatography with tandem mass spectrometry. A modified QuEChERS method with multiwalled carbon nanotubes and carbon material was adopted in the multi-Plug Filtration Cleanup procedure. This method was validated for 44 representative pesticides spiked at two concentration levels of 10 and 100 μg/kg. The pesticides of different physicochemical properties were registered on spinach in China. The recoveries were between 76 and 114% for major pesticides with relative standard deviations of less than 15%, except for quizalofop-P-ethyl, pyrimethanil, and carbendazim. Matrix-matched calibration curves were performed with the coefficients of determination higher than 0.995 for the studied pesticides for concentration levels of 10-500 μg/kg. The limits of quantitation ranged from 2 to 10 μg/kg. The developed method was successfully applied to determine pesticide residues in Chinese market spinach samples.

Analysis of sulfonamides, tilmicosin and avermectins residues in typical animal matrices with multi-plug filtration cleanup by liquid chromatography–tandem mass spectrometry detection

The frequent use of various veterinary drugs could lead to residue bioaccumulation in animal tissues, which could cause dietary risks to human health. In order to quickly analyze the residues, a liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed for detecting Sulfonamides, Tilmicosin and Avermectins (AVMs) residues in animal samples. For sample preparation, modified QuEChERS (quick, easy, cheap, effective, rugged and safe) and ultrasound-assisted extraction (UAE) methods were used. For sample cleanup, n-Hexane delipidation and multi-plug filtration cleanup (m-PFC) method based on primary-secondary amine (PSA) and octadecyl-silica (C18) were used, followed by LC-MS/MS analysis. It was validated on 7 animal matrices (bovine, caprine, swine meat and their kidneys, milk) at two fortified concentration levels of 5 and 100μg/kg. The recoveries ranged from 82 to 107% for all analytes with relative standard deviations (RSDs) less than 15%. Matrix-matched calibrations were performed with coefficients of determination above 0.998 for all analytes within concentration levels of 5-500μg/kg. The developed method was successfully used to analysis veterinary drugs of real animal samples from local markets.

Multiresidue Method for Determination of 183 Pesticide Residues in Leeks by Rapid Multiplug Filtration Cleanup and Gas Chromatography–Tandem Mass Spectrometry

This study reports the development of a novel multiplug filtration cleanup (m-PFC) procedure for analysis of pesticide residues in leek samples followed by gas chromatography-tandem mass spectrometry detection. The leek samples were initially purified following the dispersive solid-phase extraction with different sorbents to determine the most suitable proportioning of sorbent materials; then, the m-PFC method was carried out by applying the streamlined procedure with syringes. Average recoveries of most pesticides were in the range from 70.2 to 126.0% with the relative standard deviation < 20% with the m-PFC process. The limits of detection were 0.03-3.3 μg kg(-1). The limits of quantification were 0.1-10 μg kg(-1). The m-PFC process is convenient and time-efficient, taking just a few seconds per sample. Finally, the developed method was successfully applied to the determination of pesticide residues in market samples. In that analysis, 35 pesticides were detected in 29 samples, with values ranging from 2.0 to 9353.1 μg kg(-1).

Automated multi-plug filtration cleanup for liquid chromatographic–tandem mass spectrometric pesticide multi-residue analysis in representative crop commodities

An automated multi-plug filtration cleanup (m-PFC) method on modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) extracts was developed. The automatic device was aimed to reduce labor-consuming manual operation workload in the cleanup steps. It could control the volume and the speed of pulling and pushing cycles accurately. In this work, m-PFC was based on multi-walled carbon nanotubes (MWCNTs) mixed with other sorbents and anhydrous magnesium sulfate (MgSO4) in a packed tip for analysis of pesticide multi-residues in crop commodities followed by liquid chromatography with tandem mass spectrometric (LC-MS/MS) detection. It was validated by analyzing 25 pesticides in six representative matrices spiked at two concentration levels of 10 and 100μg/kg. Salts, sorbents, m-PFC procedure, automated pulling and pushing volume, automated pulling speed, and pushing speed for each matrix were optimized. After optimization, two general automated m-PFC methods were introduced to relatively simple (apple, citrus fruit, peanut) and relatively complex (spinach, leek, green tea) matrices. Spike recoveries were within 83 and 108% and 1-14% RSD for most analytes in the tested matrices. Matrix-matched calibrations were performed with the coefficients of determination >0.997 between concentration levels of 10 and 1000μg/kg. The developed method was successfully applied to the determination of pesticide residues in market samples.

Automated Multiplug Filtration Cleanup for Pesticide Residue Analyses in Kiwi Fruit (Actinidia chinensis) and Kiwi Juice by Gas Chromatography–Mass Spectrometry

To reduce labor-consuming manual operation workload in the cleanup steps, an automated multiplug filtration cleanup (m-PFC) method for QuEChERS (quick, easy, cheap, effective, rugged, and safe) extracts was developed. It could control the volume and speed of pulling and pushing cycles accurately. In this study, m-PFC was based on multiwalled carbon nanotubes (MWCNTs) mixed with primary-secondary amines (PSA) and anhydrous magnesium sulfate (MgSO4) in a packed column for analysis of pesticide residues followed by gas chromatography-mass spectrometry (GC-MS) detection. It was validated by analyzing 33 pesticides in kiwi fruit and kiwi juice matrices spiked at two concentration levels of 10 and 100 μg/kg. Salts, sorbents, m-PFC procedure, 4 mL of automated pulling and pushing volume, 6 mL/min automated pulling speed, and 8 mL/min pushing speed were optimized for each matrix. After optimization, spike recoveries were within 71-120% and <20% RSD for all analytes in kiwi fruit and kiwi juice. Matrix-matched calibrations were performed with the coefficients of determination >0.99 between concentration levels of 10 and 1000 μg/kg. The developed method was successfully applied to the determination of pesticide residues in market samples.

Residue levels of five grain-storage-use insecticides during the production process of sorghum distilled spirits.

Residue levels of dichlorvos, fenitrothion, pirimiphos-methyl, malathion and deltamethrin during sorghum distilled spirits production were examined. The analytical method for these pesticides in sorghum, fermented sorghum, rice hull and distilled spirits was validated through linearity, matrix effect, accuracy and precision, limit of quantification (LOQ) and limit of detection (LOD) parameters. The pesticide residue levels before/after each process of soaking, steaming, fermentation, and distillation were determined by gas chromatography coupled with tandem mass spectrometry (GC-MS/MS). Results showed that soaking process could obviously reduce dichlorvos residue with 87% decrease as its high vapor pressure. The steaming process reduced pesticide residues by 42-83% mainly due to evaporation or thermal degradation. Also, the fermentation could remove pesticide residues by 40-63% in favor of biological degradation. Moreover, the distillation process was proved to be effective for decreasing the pesticide residues in distilled spirits with the processing factors lower than other processes for each pesticide.