Xuesheng Li

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.

Rapid Multiplug Filtration Cleanup with Multiple-Walled Carbon Nanotubes and Gas Chromatography–Triple-Quadruple Mass Spectrometry Detection for 186 Pesticide Residues in Tomato and Tomato Products

This study reports the development and validation of a novel rapid cleanup method based on multiple-walled carbon nanotubes in a packed column filtration procedure for analysis of pesticide residues followed by gas chromatography-triple-quadruple tandem mass spectrometry detection. The cleanup method was carried out by applying the streamlined procedure on a multiplug filtration cleanup column with syringes. The sorbent used for removing the interferences in the matrices is multiple-walled carbon nanotubes mixed with anhydrous magnesium sulfate. The proposed cleanup method is convenient and time-saving as it does not require any solvent evaporation, vortex, or centrifugation procedures. It was validated on 186 pesticides and 3 tomato product matrices spiked at two concentration levels of 10 and 100 μg kg(-1). Satisfactory recoveries and relative standard deviations are shown for most pesticides using the multiplug filtration cleanup method in tomato product samples. The developed method was successfully applied to the determination of pesticide residues in market samples.

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.

Simultaneous determination of 36 pesticide residues in spinach and cauliflower by LC-MS/MS using multi-walled carbon nanotubes-based dispersive solid-phase clean-up

A multi-residue method based on a modified QuEChERS sample preparation with multi-walled carbon nanotubes (MWCNTs) as reversed-dispersive solid-phase extraction (r-DSPE) material and LC-MS/MS determination by MRM mode was validated for 36 representative pesticides in spinach and cauliflower. It was demonstrated that MWCNTs can be used as effective r-DSPE materials with the QuEChERS method for the clean-up of extract from different matrices. However, MWCNTs could absorb pyrimethanil, diflubenzuron, and chlorbenzuron in both spinach and cauliflower, which leads to the low recoveries compared with PSA. The LODs and LOQs for 36 pesticides ranged from 0.1 to 5 μg kg−1 and from 2 to 30 μg kg−1, respectively. Good linearity was found for all pesticides with coefficients better than 0.995 in a range of 0.02–0.5 mg l−1. The developed method with MWCNTs clean-up was successfully used to determine the 36 pesticides in real 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.

Multiresidue analysis of 58 pesticides in bean products by disposable pipet extraction (DPX) cleanup and gas chromatography-mass spectrometry determination.

A method based on disposable pipet extraction (DPX) sample cleanup and gas chromatography with mass spectrometric detection by selected ion monitoring (GC/MS-SIM) was established for 58 targeted pesticide residues in soybean, mung bean, adzuki bean and black bean. Samples were extracted with acetonitrile and concentrated (nitrogen gas flow) prior to being aspirated into DPX tubes. Cleanup procedure was achieved in a simple DPX-Qg tube. Matrix-matched calibrations were analyzed, and the limits of quantification (LOQ) of this method ranged from 0.01 mg kg(-1) to 0.1 mg kg(-1) for all target compounds. Coefficients of determination of the linear ranges were between 0.9919 and 0.9998. Recoveries of fortified level 0.02 mg kg(-1) on soybean, mung bean, adzuki bean and black bean were 70.2-109.6%, 69.1-119.0%, 69.1-119.8%, and 69.0-120.8%, respectively, for all studied pesticides. Moreover, pesticide risk assessment for all the detected residues in 178 market samples at Beijing market area was conducted. A maximum 0.958% of ADI (acceptable daily intake) for NESDI (national estimated daily intake) and 55.1% of ARfD (acute reference dose) for NESTI (national estimated short-term intake) indicated low diet risk of these products.

Coupling of multi-walled carbon nanotubes/polydimethylsiloxane coated stir bar sorptive extraction with pulse glow discharge-ion mobility spectrometry for analysis of triazine herbicides in water and soil samples

An analytical method based on stir bar sorptive extraction (SBSE) coupled with pulse glow discharge-ion mobility spectrometry (PGD-IMS) was developed for analysis of three triazine pesticide residues in water and soil samples. An injection port with sealing device and stir bars hold device were designed and constructed to directly position the SBSE fiber including the extracted samples into the heating device, making desorption and detection of analytes proceeded simultaneously. The extraction conditions such as SBSE solid phase material, extraction time, extraction temperature, pH value and salt concentration were optimized. Mixture of MWCNTs-COOH and PDMS were shown to be effective in enriching the triazines. The LODs and LOQs of three triazines were found to be 0.006-0.015μgkg(-1) and 0.02-0.05μgkg(-1), and the linear range was 0.05-10μgL(-1) with determination coefficients from 0.9987 to 0.9993. The SBSE-PGD-IMS method was environmentally friendly without organic solvent consumption in the entire experimental procedures, and it was demonstrated to be a commendable rapid analysis technique for analysis of triazine pesticide residues in environmental samples on site. The proposed method was applied for the analysis of real ground water, surface water and soil samples.

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).

Decrease of Pirimiphos-Methyl and Deltamethrin Residues in Stored Rice with Post-Harvest Treatment

A modified quick, easy, cheap, effective, rugged (QuEChERS) method with multi-walled carbon nanotubes (MWCNTs) as reversed-dispersive solid phase extraction (r-DSPE) material was applied to the analysis of pirimiphos-methyl and deltamethrin residues in stored rice. Two dustable powder (DP) formulations (2% pirimiphos-methyl and deltamethrin DP; 5% pirimiphos-methyl DP) were applied in simulated storehouse trials in the lab. The residues and dissipation of the two pesticides in stored rice were investigated. Slow dissipation of both pesticides was observed in stored rice. The half-lives of pirimiphos-methyl were 23.9–28.9 days, and those of deltamethrin were 23.9–24.8 days. Residues of pirimiphos-methyl from application rates of 4.5–6.75 a.i. mg/kg (active ingredient milligram per kilogram) and 10–15 a.i. mg/kg were 1.6–3.8 mg/kg and 3.0–4.5 mg/kg at 60 days Pre-harvest Interval (PHI). Residues of deltamethrin from an application rate of 0.5–0.75 a.i. mg/kg were 0.13–0.14 mg/kg at 60 days PHI. Both pesticides residues were below the Maximum Residue Limits (MRLs) established by the Codex Alimentarius Commission (CAC). Therefore, at the recommended dosages they are safe for use on stored rice.

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.