Bei Fan

Determination of inorganic arsenic in rice by solid phase extraction and hydride generation atomic fluorescence spectrometry

Inorganic arsenic (iAs) is a food safety concern worldwide due to its high toxicity, particularly in rice, which accumulates As more easily than other crops. Accordingly, low-cost, simple methods are needed for accurate determination of iAs in food crops. We extracted total arsenic (As) from rice using HNO3 and then reduced arsenate (As5+) to arsenite (As3+) using thiourea. The combined As3+ was separated from organic As using polystyrene resin cartridges, and quantified by hydride generation-atomic fluorescence spectrometry (HG-AFS). This method achieved 1.1 μg kg−1 limit of detection, 3.6 μg kg−1 limit of qualification, and <6% relative standard deviation. Validation was performed using certified reference materials and conventional high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICPMS). Compared with LC-HG-AFS or LC-ICPMS, this method appears suitable for general use because of its low cost.

Behavior of field-applied triadimefon, malathion, dichlorvos, and their main metabolites during barley storage and beer processing

The behavior and fate of 3 pesticides (triadimefon, malathion, and dichlorvos) and the main metabolites (triadimenol and malaoxon) during barley storage or beer processing were assessed using a pilot-plant equipment. The residues of all products were determined using liquid chromatography coupled with tandem mass spectrometry. Field investigation of the dissipation rate kinetics for triadimefon and malathion during storage indicated that their half-life was twice as high when 5 times the recommended dosage was used. Milling had little effect on the removal of dichlorvos and malathion residues, whereas these were substantially removed when the spent grains were filtered after mashing. The calculated processing factors were all <1, indicating the residual ratios of dichlorvos and malathion were reduced during the entire process. In conclusion, storage and processing considerably reduced pesticide residue levels in barley and beer; however, greater focus needs to be paid to the toxicity of their metabolites in commercial by-products.

Chemometric-assisted QuEChERS extraction method for post-harvest pesticide determination in fruits and vegetables

An effective analysis method was developed based on a chemometric tool for the simultaneous quantification of five different post-harvest pesticides (2,4-dichlorophenoxyacetic acid (2,4-D), carbendazim, thiabendazole, iprodione, and prochloraz) in fruits and vegetables. In the modified QuEChERS (quick, easy, cheap, effective, rugged and safe) method, the factors and responses for optimization of the extraction and cleanup analyses were compared using the Plackett–Burman (P–B) screening design. Furthermore, the significant factors (toluene percentage, hydrochloric acid (HCl) percentage, and graphitized carbon black (GCB) amount) were optimized using a central composite design (CCD) combined with Derringer’s desirability function (DF). The limits of quantification (LOQs) were estimated to be 1.0 μg/kg for 2,4-D, carbendazim, thiabendazole, and prochloraz, and 1.5 μg/kg for iprodione in food matrices. The mean recoveries were in the range of 70.4–113.9% with relative standard deviations (RSDs) of less than 16.9% at three spiking levels. The measurement uncertainty of the analytical method was determined using the bottom-up approach, which yielded an average value of 7.6%. Carbendazim was most frequently found in real samples analyzed using the developed method. Consequently, the analytical method can serve as an advantageous and rapid tool for determination of five preservative pesticides in fruits and vegetables.

Synthesis of cyclic ethers by cyclodehydration of 1,n-diols using heteropoly acids as catalysts

Heteropoly acids were used as catalysts for cyclodehydration of various 1,n-diols. Cyclodehydration of butane-1,4-diol, pentane-1,5-diol and hexane-1,6-diol catalysed by H3PW12O40 gave tetrahydrofuran, tetrahydropyran and oxepane, respectively. Cyclodehydration of diethylene glycol, triethylene glycol, diethylene glycol monomethyl ether and polyethylene glycol 200 catalysed by H3PW12O40 gave 1,4-dioxane. In particular, cyclodehydration of hexane-1,6-diol gave an excellent yield of oxepane (80%). The selectivity exhibited by the H3PW12O40 catalyst was even better than that exhibited by other reported catalyst systems for similar cyclodehydration reactions.

“Off–On” fluorescent sensing of organophosphate pesticides using a carbon dot–Au(III) complex

Herein, we report novel “off–on” fluorescent sensing of organophosphate pesticides using a carbon dot (CD)–Au(III) complex/acetylcholinesterase (AChE) system. The above sensor utilizes the quenching of CD fluorescence by Au(III) and its subsequent recovery by thiocholine, which is generated by AChE-catalyzed hydrolysis of acetylthiocholine (ATCh) and effectively scavenges Au(III). In the presence of organophosphates, the catalytic activity of AChE is inhibited, allowing these species to be quantified based on the decreased recovery of CD fluorescence intensity. The developed sensor was used to analyze a real pesticide-spiked sample (4.48 μM), achieving a recovery of 99.85% and exhibiting a linear response range of 0.45–44.80 μM.

Citrus sinensis MYB transcription factors CsMYB330 and CsMYB308 regulate fruit juice sac lignification through fine-tuning expression of the Cs4CL1 gene

Lignin is one of the most important components of the plant cell wall, and the expression and transcriptional regulation of lignin biosynthesis-related genes have been studied widely in Arabidopsis and other plants. Citrus fruit juice sacs often undergo lignification, particularly during fruit ripening and storage periods; however, the underlying genetic mechanisms have been little investigated. In this study, we isolated and identified CsMYB330 and CsMYB308 transcription factors, and found that their expression levels are significantly altered during the lignification of citrus fruit juice sacs. We found that CsMYB330 and CsMYB308 can recognize and bind AC elements in the Cs4CL1 promoter and finely regulate expression of the Cs4CL1 gene. In this regulatory process, CsMYB330 was identified as a transcriptional activator, whereas CsMYB308 appears to be a transcriptional repressor. In addition, using a transient assay, we demonstrated that expression of the Cs4CL1 gene is significantly altered in fruit juice sacs overexpressing these two transcription factors. These results indicate that the transcription factors CsMYB330 and CsMYB308 play important roles in the lignification of citrus fruit juice sacs and provide novel insights into the transcriptional regulation associated with fruit juice sac lignification.

Residue and Dietary Risk Assessment of Chiral Cyflumetofen in Apple

Ultra-performance convergence chromatography is an environmentally-friendly analytical method that uses dramatically reduced amounts of organic solvents. In addition, a robust and highly sensitive chiral separation method was developed for the novel chiral acaricide cyflumetofen by using ultra-performance convergence chromatography coupled with tandem mass spectrometry, which shows that stereoisomer recoveries determined for various apple parts ranged from 78.3% to 119.9%, with the relative standard deviations being lower than 14.0%. The half-lives of (−)-cyflumetofen and (+)-cyflumetofen obtained under 5-fold applied dosage equal to 22.13 and 22.23 days, respectively. For 1.5-fold applied dosage, the respective values were determined as 22.42 and 23.64 days, i.e., the degradation of (−)-cyflumetofen was insignificantly favored over that of its enantiomer. Importantly, cyflumetofen was unevenly distributed in apples, with its relative contents in apple peel, peduncle, and pomace equal to 50%, 22%, and 16%, respectively. The proposed method can be used to efficiently separate and quantify chiral pesticide with advantages of a shorter analysis time, greater sensitivity, and better environmental compatibility. Additionally, the consumption of apples with residue of cyflumetofen did not pose a health risk to the population if the cyflumetofen applied under satisfactory agricultural practices after the long-term dietary risk assessment.