Development of a UPLC-MS/MS-based method for simultaneous determination of advanced glycation end products and heterocyclic amines in stewed meat products.

A novel analytical strategy was proposed to simultaneously quantify two advanced glycation end products (AGEs) including Nε-(Carboxymethyl)lysine (CML), Nε-(Carboxyethyl)lysine (CEL) and eight heterocyclic amines (HAs) including IQ, MeIQ, MeIQx, 4,8-DiMeIQx, 7,8-DiMeIQx, PhIP, Harman, and Norharman. The procedure was based on a two-step extraction, solid phase extraction (SPE) purification followed by ultra performance liquid chromatography tandem mass spectrometry. The established method showed a good linearity (R2 ≥ 0.9950), rapid processing time (8 min per sample), satisfactory recoveries (matrix spiked recoveries range from 72.2% to 119.6%) and precision (intra-day and inter-day RSDs were <19.3%). The limit of quantification (LOQ) and limit of detection (LOD) resulted to be between 0.05-15 ng/g and 0.2-50 ng/g, respectively. The validated technique was further applied to determine HAs and AGEs in eight stewed meat product samples consumed in Shanghai, with the amount of HAs and AGEs ranging from 2.851 to 18.289 ng/g and 118.158-543.493 ng/g, respectively.

Residue behaviors, degradation, processing factors, and risk assessment of pesticides in citrus from field to product processing.

Pesticide residues in citrus may cause health risks in related juice products, and bring much uncertainty during the processing procedures. In this study, based on the dispersive solid-phase extraction (d-SPE) and UPLC-MS/MS, the residual levels of ten analytes in citrus and its processed products were monitored. The results showed that dissipation of the pesticides followed the first-order kinetics and the half-lives in citrus varied greatly, ranging from 6.36 to 63.0 days. The terminal residues of the five pesticides at harvest time were <0.01-0.302 and <0.01-0.124 mg/kg in raw citrus and citrus flesh, respectively, all of which were lower than the corresponding maximum residue limits (MRLs) of 0.5-1 mg/kg. In the processing experiments, the residues of ten analytes in sterilized juice, concentrated juice, and citrus essential oil were in the range of <0.01 to 0.442 mg/kg, <0.01 to 1.16 mg/kg, and <0.01 to 44.0 mg/kg, respectively, and the corresponding processing factors (PFs) were 0.127-1.00, 0.023-3.06, and 0.006-39.2. Particularly, in citrus essential oil, the PFs of etoxazole, fluazinam, lufenuron and spirotetramat-keto-hydroxy were 1.68-39.2, exhibiting obvious enrichment effects. By integrating the residue data of the field trials and the PFs, the acute and chronic dietary risks of the target pesticides in citrus juice were 0.031-1.83 % and 0.002-2.51 %, respectively, which were far lower than 100 %, demonstrating no unacceptable risk to human health. This work provides basic data for the establishment of the MRLs and dietary exposure risk assessment for processed citrus products.

Long-Distance Wind Dispersal Drives Population Range Expansion of Solidago canadensis.

Canada goldenrod (Solidago canadensis L.) is a serious invasive alien plant species that exerts negative effects on natural and agricultural ecosystems in China. Few studies have addressed the dispersal of S. canadensis to explain how it rapidly spreads to large areas over long distances. Here, we quantify the dispersal of S. canadensis via wind by capturing in situ-stained diaspores. The diaspores were trapped and counted along 11 radiating transects from the center of a dispersal source. Solidago canadensis diaspores could be dispersed in all directions from the source, traveling longer distances and in greater amounts in the downwind direction than the upwind one. With a source including about 58 million diaspores and a wind speed at Beaufort scale 4, the dispersal distance in the prevailing wind direction (PWD) was at least 2000 m. Diaspores shattered at a rate of approximately 3% daily with the common wind speed of scale 4, indicating that dispersal could last for more than a month. A mechanistic model was used to fit the dispersal curve along the PWD. Although the model slightly underestimated long-distance dispersal, it still demonstrated the potential of long-distance dispersal with great source strength. Wind-dispersed diaspores to new areas persisted over winter and were able to form new plants at a density of about 2 plants per m2 at 500 m away from the source. Further experiments showed that the dispersed amount of S. canadensis diaspores was significantly positively correlated with the temperature and wind speed, but significantly negatively correlated with relative humidity, which indicated that, during a day, the maximum dispersal usually occurred in the afternoon when the temperature was the highest and the relative humidity the lowest. In addition, for an already existent population patch, the patch range can expand 2-4 m per year, mainly depending on the seedlings recruited from the rhizomes. These results provide insights into the long-distance dispersal of S. canadensis by wind and its effects on the range expansion process.

[Determination of disulfoton and its metabolites in agricultural products by dispersive soild phase extraction-ultra high performance liquid chromatography-tandem mass spectrometry].

Disulfoton, an organophosphorus pesticide, is used to control cotton, beet, potato, and other seedling period aphids, leaf moths, underground pests, etc., with internal absorption, killing, gastric poisoning, and fumigation. Disulfoton is a highly toxic organophosphate pesticide, which can inhibit cholinesterase activity, resulting in neurophysiological disorders by inhalation, feeding, and transdermal absorption. Disulfoton is difficult to degrade in the environment, which leads to enrichment in organisms and interference with endocrine. This compound is harmful to the ecological environment and human health. To ensure the quality and safety of food, it is important to develop a detection method for disulfoton and its metabolites in agricultural products. A reliable method based on dispersive solid phase extraction (d-SPE) with ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was developed for the determination of disulfoton and its metabolites (disulfoton sulfone, disulfoton sulfoxide, demeton-S, demeton-S sulfone, and demeton-S sulfoxide) in agricultural products (pea, asparagus, wheat, coffee bean, and peanut). The optimal extraction method was as follows: 5.0 g the samples were extracted with acetonitrile (wheat, coffee bean, and peanut presoaked in 5 mL water) in a 50 mL centrifuge tube, followed by 10 min vortex. Before 30 s vortex, 4 g NaCl was added. After 5 min centrifugation, 1.5 mL of the supernatant was cleaned up with 50 mg octadecylsilane bonded silica (C18), 50 mg primary secondary amine (PSA), and 50 mg aminopropyl (NH2) adsorbents. The analytes were separated on a Thermo Syncronis C18 column (150 mm×2.1 mm, 5 µm) with gradient elution using water and acetonitrile at a column temperature of 40 ℃. The injection volume was 2 µL. Disulfoton and its metabolites were analyzed in multiple reaction monitoring (MRM) mode with positive electrospray ionization (ESI+) for the selective quantification. Qualitative and quantitative analyses were accorded to the retention times and characteristic ion pairs with one parent ion and two fragment ions. Quantitative analysis was performed by an external standard method using matrix-matched calibration curves. All the parameters that affected the extraction efficiencies were optimized. C18, PSA, and NH2 gave good recoveries of 87.9%-109.0%. Other adsorbents, multiwalled carbon nanotubes (MWCNTs), hydroxylated multiwalled carbon nanotubes (OH-MWCNTs), carboxylated multiwalled carbon nanotubes (COOH-MWCNTs), octylsilane bonded silica (C8), strong cation exchange (SCX) and neutral alumina (N-Al2O3), led to recoveries below 56.2%. The combination of adsorbents was also considered. Seven different combinations of 50 mg C18, 50 mg PSA, and 50 mg NH2 were chosen for the optimization experiments. There were no obvious differences in these combinations, and the target analytes recoveries ranged from 81.0% to 109.3% with relative standard deviations (RSDs) between 0.6% and 12.5%. The matrix effect could affect the extraction efficiency. The adsorbents of 50 mg C18, 50 mg PSA, and 50 mg NH2 showed weaker matrix effects as compared with other combinations of adsorbents in the instrument. The results for the matrix effect showed that peanuts and asparagus exceeded 20%, requiring matrix-matched calibration curves. Under the optimized conditions, disulfoton and its metabolites showed good linearities (R2≥0.9981) in the range of 2.0-200.0 µg/L. The average spiked recoveries of disulfoton and its metabolites in peas, asparagus, wheat, peanuts, and coffee beans ranged from 75.0% to 110.0%, with RSDs of 0.7% to 14.9%. The limits of detection (LODs) were between 0.02 and 2.0 µg/kg, and the limits of quantification (LOQs) were 5.0 µg/kg. The method was applied for the detection of 80 commercial productions, and neither disulfoton nor its metabolites were found. The proposed method is rapid, accurate, highly selective, and sensitive, and it is suitable for the simultaneous determination of disulfoton and its metabolites in grain, oil crops, vegetables, and other matrices.

Determination of 1-methylcyclopropene residues in vegetables and fruits based on iodine derivatives.

An innovative method was established for the determination of 1-methylcyclopropene (1-MCP) in vegetables and fruits. Due to its small molecular weight and low boiling point, it was difficult to obtain quantitative analysis for 1-MCP, especially at the residual level. In this work, based on its iodine derivatives, 1-MCP was derived to 1,2-diiodo-1-methylcyclopropane, which was much easier for trace and accurate chromatographic analysis. During the method validation, the method validation results were satisfactory in terms of linearity (4 ~ 400 µg/L, and R2 ≥ 0.959), matrix effect (-89% ~ -13%), accuracy (80 ~ 100%), sensitivity (limits of quantification, 5 µg/kg) and precision (relative standard deviations ≤ 19%), which was in accordance with the Chinese guidelines for the testing of pesticide residues in crops. Finally, the proposed analytical method was used to monitor the 1-MCP residue levels in commercially available samples, and all the values were below 5 µg/kg, which satisfied the EU or Japan MRLs of 1-MCP.

Residue behavior and dietary risk assessment of six pesticides in pak choi using QuEChERS method coupled with UPLC-MS/MS.

A reliable and simple modified QuEChERS method with UPLC-MS/MS was developed for the simultaneous determination of six pesticides (dimethomorph, imidaclothiz, lufenuron, methoxyfenozide, pyridaben, spinetoram) and their metabolites in pak choi. Method validation indicated good linearity (R2 ≥ 0.99), accuracy (recoveries of 75%-112%), sensitivity (limits of quantification, 0.002-0.01 mg kg-1), and precision (relative standard deviations ≤ 21%), and matrix effects were -36-28%. The half-lives of the six pesticides in pak choi were 2.2-12 d under open field and greenhouse conditions. Considering the short growth cycle of pak choi, the terminal residue levels (0.046-7.8 mg kg-1) and the relevant maximum residue limits (MRLs) of some countries, 5 d was recommended as the pre-harvest interval for the six pesticides on pak choi. Dietary risk assessment revealed that the risk quotients were 3.1%-58% for different gender and age groups in China, indicating none unacceptable public health risk for general population. The results showed that all the six pesticides degraded faster and the terminal residues were much lower under open field conditions than those under greenhouse conditions, which was mainly due to the influence of rainfall, sunlight and other environmental factors. This work was thus significant in assessing the dissipation fate and food safety risks of the six pesticides on pak choi and facilitated the establishment of maximum residue limits.

Dissipation and safety evaluation of novaluron, pyriproxyfen, thiacloprid and tolfenpyrad residues in the citrus-field ecosystem.

The dissipations and residues of four pesticides in citrus, under field conditions, were measured using solid-phase extraction and LC-MS/MS. In the method validation, satisfactory results were obtained with fortified recoveries ranging from 80.6 to 113% and relative standard deviations ≤9.0%. In the dissipation test, the half-lives for the pesticides in citrus, according to first-order kinetics, ranged from 13.3 to 28.9 days. Based on the terminal residue test, two evaluation models (hazard quotient, HQ; risk quotient, RQ) were applied on citrus fruits for dietary exposure risk assessment. The results showed that HQs ranged from 0.0031 to 0.78%, and RQs from 7.3 to 57%, which are both acceptable for human consumption. Therefore, 14-day was proposed as a pre-harvest interval for the target compounds in citrus fruits. This work also contributes to residue data and, therefore, scientifically validated maximum residue limits in citrus, which are lacking in China currently.