Stereoselective behaviors and enantiomeric effects of paclobutrazol on microorganisms during Chinese cabbage pickling process.

Studies on the differences between chiral pesticide enantiomers have caused widespread concern in the last decade. In the current work, the selective behaviors and different biological activities of paclobutrazol enantiomers during Chinese cabbage pickling process were evaluated. Results of degradation kinetics indicated that when paclobutrazol reside in raw material (Chinese cabbage) and was introduced into the pickling process, the degradation rates of the two paclobutrazol enantiomers were significantly different, the half-lives of (2R, 3R)-paclobutrazol (R-paclobutrazol) and (2S, 3S)-paclobutrazol (S-paclobutrazol) were 18.24 and 6.19 d, respectively. Besides, the conversion between the two enantiomers could also be observed, and the conversion rate of R-paclobutrazol to S-paclobutrazol was slower than that of reverse process. In addition, from the analysis of 16S rRNA and ITS sequencing, we inferred that the degradation of paclobutrazol was probably due to the presence of Pseudomonas and Serratia. Moreover, there has a significant difference in biological activity between R-paclobutrazol and S-paclobutrazol and shown an obviously enantiomeric effects on microbial community composition of pickling system. Besides, the analysis of microbial community displayed R-paclobutrazol might inhibit the growth of Erwinia (a sort of plant pathogens). Results from this study served to enhance our understanding of chiral pesticide residues on food safety and the potential risks to human health.

High-throughput determination of fungicides in grapes using thin-film microextraction coupled with liquid chromatography-tandem mass spectrometry.

A high-throughput and environmentally friendly method based on 96-well plate thin-film microextraction was established to determine 14 fungicides in grapes and grape juice using liquid chromatography-tandem mass spectrometry. The thin-film microextraction optimized method consisted of 60 min of extraction at pH 6.0 with the addition of sodium chloride (2-5%). Acetonitrile/water in the ratio of 8:2 was used for desorption analytes for 60 min. Evaluation of different extractive phases showed that polyacrylonitrile-polystyrene-divinylbenzene was the optimum coating. The linearity of the method was good in the range of 0.01-0.5 µg/mL for 14 fungicides with determination coefficients (R2 ) from 0.990 to 0.999, which indicated good linearity for both the grape juice and grape matrixes. The limit of detection was in the range of 0.002-0.01 µg/mL. The limit of quantitation was in the range of 0.01 mg/kg according to the minimum fortified level. The average absolute recoveries of the 14 fungicides ranged from 75.0 to 118.3%. The intraday relative standard deviation (n = 4) and interday relative standard deviation (n = 4) were 5.6-13.0% and 1.6-6.4%, respectively. This study showed that this method can be used for analyzing 96 samples in parallel, and the sample preparation time was approximately 2.0 min per sample. In addition, this approach offers a green and low-cost sample pretreatment technique for future analyses.

[QuEChERS-liquid chromatography-tandem mass spectrometry for determination of 22 triazole pesticide residues in Chinese herbal medicines].

Eight well-known herbals in Zhejiang Province, Zhebawei, are commonly used as traditional Chinese herbal medicines owing to their rich active ingredients. However, the unavoidable use of pesticides during agricultural production has led to pesticide residue problems in these herbs. In this study, a simple, rapid, and accurate method was established to determine 22 triazole pesticide residues in Zhebawei. An improved QuEChERS method was used for sample pretreatment, and Rhizoma Atractylodis Macrocephalae was used as a representative sample. The sample was extracted with acetonitrile to eliminate some polar and nonpolar compounds, pigments, and other impurities, and the purification effects of multiwalled carbon nanotubes (MWCNTs), amino-modified multiwalled carbon nanotubes (MWCNTs-NH2), carboxylated multiwalled carbon nanotubes (MWCNTs-COOH), crosslinked polyvinylpyrrolidone (PVPP), zirconium dioxide (ZrO2), 3-(N,N-diethylamino)-propyltrimethoxysilane (PSA), octadecyl (C18), and graphitized carbon black (GCB) were compared. MWCNTs-COOH and C18 were selected as the purification adsorbents, and their dosages were systematically optimized. The combination of 10 mg of MWCNTs-COOH and 20 mg of C18 was eventually selected as the purification adsorbents. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used for analysis, and box graphs were plotted to present the dispersion of each group of recoveries, thus enabling the identification of the data outliers, dispersion distribution, and data symmetry. The established method was systematically verified and showed good linearity over the concentration range of 1-200 µg/L (except for bromuconazole, epoxiconazole, and etaconazole) with correlation coefficients >0.99. The average recoveries of the 22 pesticides at spiked levels of 10, 20, 100, and 200 µg/kg were in the range of 77.0%-115% with relative standard deviations (RSDs) <9.4%. The limits of detection and quantification were 1-2.5 µg/kg and 10-20 µg/kg, respectively. The applicability of the developed method to other herbals was investigated at 100 µg/kg, and the average recoveries of the target pesticides in different matrices ranged from 76.4% to 123% with RSDs <12.2%. Finally, the method established was used to detect triazole pesticide residues in 30 actual Zhebawei samples. The results showed that triazole pesticides were present in Bulbus Fritillariae Thunbergii and Dendranthema Morifolium. Difenoconazole was detected in Bulbus Fritillariae Thunbergii at contents ranging from 41.4 µg/kg to 110 µg/kg, while difenoconazole, myclobutanil, triadimenol and propiconazole were detected in Dendranthema Morifolium at contents ranging from 16.1 µg/kg to 250 µg/kg. The established method can meet the requirements for the accurate quantitative analysis of triazole fungicides in Zhebawei.

Magnetic covalent organic framework as a solid-phase extraction absorbent for sensitive determination of trace organophosphorus pesticides in fatty milk.

A simple and efficient magnetic solid-phase extraction (MSPE) method was established with magnetic covalent organic framework (COF) as adsorbent to enrich organophosphorus pesticides from fatty milk samples, followed by the sensitive determination via LC-MS/MS. The key parameters influencing the MSPE efficiency were comprehensively investigated to afford an optimized procedure. All the target analytes could be captured directly by magnetic COF from milk without protein precipitation, making the pretreatment rapid and convenient. Systematic method validation demonstrated its satisfactory linearity, recoveries (80.0-105 %), and precision (RSDs <12.3 %). The method limits of quantification were 0.2-0.5 µg L-1. A comparison experiment to the reported solid-phase extraction fully verified the present MSPE more rapid, accurate, and environment-friendly. Furthermore, FT-IR and XPS analysis were performed to reveal the adsorption mechanisms of magnetic COF to organophosphorus pesticides, which could offer guidance on the rational design of COF adsorbent for various target analytes.