Thiamethoxam dynamics in pepper plants: Deciphering deposition and dissipation pattern across diverse planting modes and regions.

To reduce the application dosage of thiamethoxam (TMX), we investigated the deposition and dissipation patterns in a pepper-planted ecosystem under different planting modes across four regions in China, namely Hainan (HN), Zhejiang (ZJ), Anhui (AH) and Hebei (HB). This study focused on the deposition and dissipation of TMX at concentrations of 63.00, 47.25, 31.50, 23.63 and 15.75 g a.i.hm-2. As the application dose increased, the deposition amount of TMX initially increased in the plants and cultivated soil, showing obvious geographic differences in four cultivation areas. Surprisingly, the initial amount of TMX deposited the pepper-cultivated greenhouse of ZJ and AH was 1.1-2.1-fold and 1.0-3.6-fold higher than that in the open field system at the same application dose, respectively. In pepper leaves, stems, fruits and soil, the dissipation exhibited rapid growth and then slowed. However, the residual concentration showed an increasing trend, followed by a subsequent decrease in the pepper roots. In different planting regions, the dissipation rate of TMX followed the order HN > ZJ > AH > HB in pepper plants and cultivated soil. In comparison to the open field, the total TMX retention rate in greenhouse was higher, indicating overall greater persistence in the greenhouse conditions. These findings reveal the deposition and dissipation characteristics of TMX within the pepper-field ecosystem, offering a significant contribution to the risk assessment of pesticides.

Transfer assessment of carbendazim residues from rapeseed to oil production determined by HPLC-MS/MS.

It is crucial to develop practical procedures for the control and reduction of pesticide residues in oil productions from farm to dining table. In this study, the dissipation behaviors of typical fungicide from rapeseed to oil production were studied to reveal relationship among spraying stage, application dosage, household oil processing stage, and pesticide residues. In the field trials, rape plants were sprayed with carbendazim at three different dosages during flowering period. Transfer assessment of carbendazim residues from rapeseed to oil production during household oil processing via different press techniques was determined using high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS). The recoveries of carbendazim in rapeseed samples, meals after squeezing samples, and rapeseed oil samples ranged from 82.5% to 93.6% with relative standard deviations (RSDs) ＜5.2%. The validation results illustrated that the methods were reliable and sensitive. The average processing factor (PF) during household oil processing via hot press technique and cold press technique was 0.15 and 0.51, respectively. This study demonstrated that household oil processing could significantly reduce the pesticide residues, especially by hot press technique.

Etoxazole is Metabolized Enantioselectively in Liver Microsomes of Rat and Human in Vitro.

Acaricide etoxazole belongs to the ovicides/miticides diphenyloxazole class, affecting adults to lay sterile eggs by inhibiting chitin biosynthesis possibly. The reverse-phase HPLC-MS/MS method was used to determine the etoxazole enantiomers. The enantioselective degradation behavior of rac-etoxazole in liver microsomes of rat and human in vitro with NADPH was dramatically different. The t1/2 of (R)-etoxazole was 15.23 min in rat liver microsomes and 30.54 min in human liver microsomes, while 21.73 and 23.50 min were obtained for (S)-etoxazole, respectively. The Vmax of (R)-etoxazole was almost 5-fold of (S)-etoxazole in liver microsomes of rat in vitro. However, the Vmax of (S)-etoxazole was almost 2-fold of (R)-etoxazole in liver microsomes of human in vitro. The CLint of etoxazole was also shown the enantioselectivity on the contrary in liver microsomes of rat and human. These results indicated that the metabolism of two etoxazole enantiomers was selective in liver microsomes of rat and human in vitro, and enantioselectivity in the two kinds of liver microsomes was in the difference in degradation performance. The reason might be related to the composition and content involved in the enzyme system.

Simultaneous enantioselective determination of triadimefon and its metabolite triadimenol in edible vegetable oil by gel permeation chromatography and ultraperformance convergence chromatography/tandem mass spectrometry.

A novel, sensitive, and efficient enantioselective method for the determination of triadimefon and its metabolite triadimenol in edible vegetable oil, was developed by gel permeation chromatography and ultraperformance convergence chromatography/tandem triple quadrupole mass spectrometry. After the vegetable oil samples were prepared using gel permeation chromatography, the eluent was collected, evaporated, and dried with nitrogen gas. The residue was redissolved by adding methanol up to a final volume of 1 mL. The analytes of six enantiomers were analyzed on Chiralpak IA-3 column (150 × 4.6 mm) using compressed liquid CO2-mixed 14 % co-solvents, comprising methanol/acetonitrile/isopropanol = 20/20/60 (v/v/v) in the mobile phase at 30 °C, and the total separation time was less than 4 min at a flow rate of 2 mL/min. Quantification was achieved using matrix-matched standard calibration curves. The overall mean recoveries for six enantiomers from vegetable oil were 90.1-97.3 %, with relative standard deviations of 0.8-5.4 % intra-day and 2.3-5.0 % inter-day at 0.5, 5, and 50 µg/kg levels. The limits of quantification were 0.5 µg/kg for all enantiomers based on five replicate extractions at the lowest fortified level in vegetable oil. Moreover, the absolute configuration of six enantiomers had been determined based on comparisons of the vibrational circular dichroism experimental spectra with the theoretical curve obtained by density functional theory calculations. Application of the proposed method to the 40 authentic vegetable oil samples from local markets suggests its potential use in enantioselective determination of triadimefon and triadimenol enantiomers. Graphical Abstract Chemical structures and UPC(2)-MS/MS separation chromatograms of triadimefon and triadimenol.

Enantioselective determination of acaricide etoxazole in orange pulp, peel, and whole orange by chiral liquid chromatography with tandem mass spectrometry.

An efficient enantioselective method for the determination of etoxazole in orange pulp, peel, and whole orange was developed using liquid chromatography with tandem mass spectrometry. The enantioseparation was performed on a Chiralpak AD-3R column at 30ºC using acetonitrile with 0.1% formic acid solution (80:20, v/v) as the mobile phase in less than 5 min. Quantification was achieved using matrix-matched standard calibration curves. The overall mean recoveries for two enantiomers from orange pulp and whole orange were 91.0-99.6% and the orange peel was 92.6-103.1%, with relative standard deviations of 0.8-5.4% intraday and 2.0-4.8% interday at 1, 10, and 100 µg/kg levels, and 1.3-5.2% intraday and 3.5-4.3% interday at 5, 50, and 500 µg/kg levels, respectively. The limits of quantification for all enantiomers in three matrices did not exceed 5 µg/kg. Moreover, the absolute configuration of etoxazole enantiomers had been determined by the combination of experimental and predicted electronic circular dichroism spectra, and the first eluted enantiomer was confirmed as (S)-etoxazole on a Chiralpak AD-3R column while (R)-etoxazole was first on three cellulose chiral columns. The application of the proposed method to real sample analysis suggests its potential use in enantioselective determination of etoxazole enantiomers in citrus.

Simultaneous enantioselective determination of isocarbophos and its main metabolite isocarbophos oxon in rice, soil, and water by chiral liquid chromatography and tandem mass spectrometry.

An efficient enantioselective method for the simultaneous determination of isocarbophos and its main metabolite isocarbophos oxon in rice, soil, and water was developed using liquid chromatography with tandem mass spectrometry. The enantioseparation was performed on a Chiralpak AD-3R column at 30°C using gradient elution. Target compounds were extracted from soil and rice using acetonitrile with omission of a clean-up procedure, while a C18 solid-phase extraction column was used for water samples. Quantification was achieved using matrix-matched calibration. The overall mean recoveries for isocarbophos and isocarbophos oxon enantiomers from the five matrices were 89.7-103 and 90.1-98.7%, with relative standard deviations of 2.1-5.4 and 2.5-4.7%, respectively. Moreover, the absolute configurations of isocarbophos oxon enantiomers were determined by liquid chromatography with tandem mass spectrometry through incubation of each isocarbophos enantiomer in soil, the first eluting enantiomer being confirmed as (R)-(-)-isocarbophos oxon. The proposed method was applied to real soil samples and satisfactory results were obtained.

Comparative study on secondary metabolites from different citrus varieties in the production area of Zhejiang.

To investigate the distribution pattern of bioactive components and their correlations between citrus varieties, we thoroughly analyzed secondary metabolites (including flavonoids, phenolic acids, carotenoids, and limonoids) in the peel and pulp of 11 citrus varieties from the production area of Zhejiang. Citrus peels accumulated metabolites far more than the pulp, and the accumulation varied significantly between species. Flavonoids were the most abundant compounds, followed by phenolic acids, with carotenoids and limonoids being far less abundant than the first two, but limonoids were more abundant than carotenoids. Hesperidin was the main flavonoid in most varieties, but cocktail grapefruit and Changshanhuyou contained naringin, with Ponkan having the most abundant polymethoxylated flavones (PMFs). The major components of phenolic acids, carotenoids, and limonoids were ferulic acid, ß-cryptoxanthin, and limonin, respectively. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) indicated that these components were mostly correlated with each other, and these citrus varieties could be categorized into four groups by pulp and three groups by peel. The obtained results filled the data gap for secondary metabolites from local citrus and could provide data references for citrus resource utilization, selection and breeding of superior varieties, and other research.

Chiral Determination of Naringenin by Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry and Application in Citrus Peel and Pulp.

A chiral separation method of naringenin in citrus pulp and peel was established using ultra-performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS) in this study. The liquid-phase conditions for separation were Chiralpak IG-3 column at 40°C, mobile phase of methanol, and 0.1% formic acid solution (85/15; v/v). Isovolumetric elution can complete the detection within 5 min. Considering the matrix effect, the matrix standard calibration curve was used for sample quantification. Quantitation was achieved by fitting a calibration curve using a standard matrix. The mean overall recoveries of the two enantiomers from orange pulp were 91.0-110.0% and orange peel were 85.3-110.3%, with relative standard deviations of 1.5-3.8 and 0.9-3.6% at the 0.5, 2.5, 50, and 250 µg/kg levels, respectively. The limit of quantification for all enantiomers in the citrus matrix did not exceed 0.5 µg/kg. Furthermore, the absolute configuration of the naringenin enantiomer was determined by combining experimental and predicted electron circular dichroism spectroscopy, and it was confirmed on a Chiralpak IG-3 column that the first eluting enantiomer was (S)-naringenin. The determination of chiral naringenin content in actual citrus samples showed that the naringenin content in hybrid citrus and citrus pulp was significantly higher than that in pomelo. The method established in this study can be used for the determination of naringenin enantiomers in citrus, which is beneficial to variety selection.

[Rapid screening of 176 pesticide residues in vegetables by ultra fast liquid chromatography-tandem mass spectrometry].

A multiresidue analytical method for rapid screening of 176 pesticide residues in vegetables was developed by using ultra fast liquid chromatography-tandem mass spectrometry (UFLC-MS/MS). The vegetable samples were extracted by acetonitrile. It is not necessary for the extract to make a further purification after salting out. Multiple reaction monitoring with information-dependent acquisition of enhanced product ion (MRM-IDA-EPI) was used for the analysis. Based on EPI spectra and chromatographic peak area, identification and quantification of the 176 pesticide residues in vegetables were carried out by using library search technique. All the pesticides had the good linearity within their respective linear ranges (r > 0.99). The average recoveries of the 174 pesticides except for carbosulfan and cyromazine were in the range of 72.4% to 126.4% with the relative standard deviations (RSDs) from 1.0% to 18.7%. The limits of detection and quantification of the method were 0.005 - 2.0 microg/kg and 0.1 - 10 microg/kg, respectively. The results demonstrated that the method has distinct advantages of rapid speed, high sensitivity and good accuracy. Therefore, this method is suitable for the rapid screening of pesticide residues in vegetables.