Supercritical fluid chromatography separation of chiral pesticides: Unique capabilities to study cyhalothrin and metalaxyl as examples

Chiral Herbicide Fluorochloridone: Absolute Configuration, Stereoselective Bioactivity, Toxicity, and Degradation in the Potatoes

Fluorochloridone (FLC) is a chiral herbicide that has four stereoisomers. This study systematically assessed the stereoselectivity of FLC to reveal the selective environmental behavior of its four isomers. Absolute configuration confirmation, evaluation of stereoselective bioactivity toward monocotyledonous and dicotyledonous weeds, toxicity to Danio rerio, and the stereoselective degradation in the potato system under field conditions of FLC were conducted. The four FLC stereoisomers were effectively separated on a superchiral S-AD column. The absolute configurations of the four stereoisomers of FLC were confirmed as (-)-(3S, 4S), (+)-(3S, 4R), (-)-(3R, 4S), and (+)-(3R, 4R)-FLC using single-crystal X-ray diffraction. The activities of the four stereoisomers were in the order of (-)-(3S, 4S)-FLC > (+)-(3R, 4R)-FLC > (+)-(3S, 4R)-FLC > (-)-(3R, 4S)-FLC, and the rate of selective degradation were in the order of (-)-(3R, 4S)-FLC > (+)-(3R, 4R)-FLC > (-)-(3S, 4R)-FLC > (+)-(3S, 4S)-FLC. The toxicity of the isomers were in the order of (-)-(3R, 4S)-FLC > (+)-(3R, 4R)-FLC > (-)-(3S, 4S)-FLC > (+)-(3S, 4R). Based on the results of bioactivity, toxicity, and degradation behavior assessments, the stereoisomer mixture containing (3R,4R)-FLC and (3S,4S)-FLC was concluded to be a better option than racemic FLC for increasing bioactivity and reducing usage.

Strategies for chiral separation: from racemate to enantiomer

Chiral separation has become a crucial topic for effectively utilizing superfluous racemates synthesized by chemical means and satisfying the growing requirements for producing enantiopure chiral compounds. However, the remarkably close physical and chemical properties of enantiomers present significant obstacles, making it necessary to develop novel enantioseparation methods. This review comprehensively summaries the latest developments in the main enantioseparation methods, including preparative-scale chromatography, enantioselective liquid-liquid extraction, crystallization-based methods for chiral separation, deracemization process coupling racemization and crystallization, porous material method and membrane resolution method, focusing on significant cases involving crystallization, deracemization and membranes. Notably, potential trends and future directions are suggested based on the state-of-art "coupling" strategy, which may greatly reinvigorate the existing individual methods and facilitate the emergence of cross-cutting ideas among researchers from different enantioseparation domains.

Enantioselective Behaviors of Chiral Pesticides and Enantiomeric Signatures in Foods and the Environment

Unreasonable application of pesticides may result in residues in the environment and foods. Chiral pesticides consist of two or more enantiomers, which may exhibit different behaviors. This Review intends to provide progress on the enantioselective residues of chiral pesticides in foods. Among the main chiral analytical methods, high performance liquid chromatography (HPLC) is the most frequently utilized. Most chiral pesticides are utilized as racemates; however, due to enantioselective dissipation, bioaccumulation, biodegradation, and chiral conversion, enantiospecific residues have been found in the environment and foods. Some chiral pesticides exhibit strong enantioselectivity, highlighting the importance of evaluation on an enantiomeric level. However, the occurrence characteristics of chiral pesticides in foods and specific enzymes or transport proteins involved in enantioselectivity needs to be further investigated. This Review could help the production of some chiral pesticides to single-enantiomer formulations, thereby reducing pesticide consumption as well as increasing food production and finally reducing human health risks.

The 2021 European Union report on pesticide residues in food

Under European Union legislation (Article 32, Regulation (EC) No 396/2005), EFSA is to provide an annual report assessing the pesticide residue levels in foods on the European market. In 2021, 96.1% of the overall 87,863 samples analysed fell below the maximum residue level (MRL), 3.9% exceeded this level, of which 2.5% were non-compliant, i.e. samples exceeding the MRL after accounting for the measurement uncertainty. For the EU-coordinated multiannual control programme subset, 13,845 samples were analysed of which 2.1% exceeded the MRL and 1.3% were non-compliant. To assess acute and chronic risk to consumer health, dietary exposure to pesticide residues was estimated and compared with available health-based guidance values (HBGVs). A new pilot methodology based on probabilistic assessment was introduced to provide the probability of subjects being expose to an exceedance of the HBGV. Recommendations to risk manager are given to increase the effectiveness of European control systems and to ensure a high level of consumer protection throughout the EU.

Advanced Tool for Chiral Separations of Anionic and Zwitterionic (Metalla)carboranes: Supercritical Fluid Chromatography

The continuous expansion of research in the field of stable carboranes and their wide potential in the drug design require carrying out fundamental studies regarding their chiral separations. Although supercritical fluid chromatography (SFC) is a viable technique for fast enantioseparations, no investigation concerning boron cluster compounds has been done yet. We aimed at the development of a straightforward method enabling chiral separations of racemic mixtures of anionic cluster carboranes and metallacarboranes that represent an analytical challenge. The fast gradient screening testing nine polysaccharide-based columns was used. The key parameters affecting the selectivity were the type of chiral selector, the type of alcohol, and the base in cosolvent. Moreover, the addition of acetonitrile or water to the cosolvent was identified as an effective tool for decreasing the analysis time while preserving the resolution. After the optimization, the chiral separations of 19 out of 20 selected compounds were achieved in less than 10 min. These results demonstrate the clear advantage of SFC over chiral separations using HPLC in terms of both analysis time and structural variety of successfully separated compounds.

Evaluation of chiral triticonazole in three kinds of fruits: enantioseparation, degradation, and dietary risk assessment

The enantioselective behaviors of chiral pesticides would affect the accuracy of risk assessment. This study evaluated the enantioselectivity of chiral triticonazole (a widely used fungicide) in three kinds of fruits. Firstly, the enantioseparation of triticonazole enantiomers was carried out within 1.2 min utilizing CHIRALPAK OJ-3 column with a mixture of CO₂ and methanol (93:7, v/v) using SFC-MS/MS. Secondly, field trials were conducted to clarify the enantioselective degradation and residue of S-( +)-triticonazole and R-(-)-triticonazole in fruits. The initial concentrations of rac-triticonazole were 25.1-93.1 ng/g, and enantioselective degradation was observed in pear, peach, and jujube after 2 h, 10 days, and 3 days, respectively. The degradation of S-( +)-triticonazole was fastest in pear (T_1/2, 2.01 days), while the T_1/2 of R-(-)-triticonazole was 5.02 days. The residue concentrations of rac-triticonazole were less than the MRL set by EU (10 ng/g) on the 3rd and 21st day in pear and peach, respectively, which were lower than 10 ng/g in jujube on the 30th day (no MRL). Finally, we found that the dietary intake risks of rac-triticonazole in fruits were low for 2-7 age, 20-50 age/female, and 20-50 age/male. The current study could provide complimentary references for the rational usage, MRL formulation, and risk assessment of chiral triticonazole.

Enantioselective monitoring chiral fungicide mefentrifluconazole in tomato, cucumber, pepper and its pickled products by supercritical fluid chromatography tandem mass spectrometry

A fast, effective, and environmental-friendly method was developed for enantioseparation and analysis of mefentrifluconazole in vegetables based on supercritical fluid chromatography tandem mass spectrometry. The enantioselective behaviors of mefentrifluconazole enantiomers in tomato, cucumber, and pepper in the greenhouse, and pickled cucumber and pepper during processing were investigated. Mefentrifluconazole enantiomers could obtain baseline separation within 2 min. The average recoveries of all matrices ranged from 78.4% to 119.0%, with relative standard deviations less than 16.8% for two enantiomers. S-(+)-mefentrifluconazole was preferentially degraded in pepper, while there was no enantioselectivity in tomato and cucumber under field conditions. During processing, S-(+)-mefentrifluconazole was reduced preferentially than R-(-)-mefentrifluconazole in pickled cucumber and cucumber brine. Inversely, R-(-)-mefentrifluconazole degraded faster than S-(+)-mefentrifluconazole in pepper brine. But, no obvious enantioselectivity was observed in pickled pepper. The result of this study could contribute to a more accurate dietary risk assessment of mefentrifluconazole in vegetables and processed products.

Liquid chromatography versus supercritical fluid chromatography coupled to mass spectrometry: a comparative study of performance for multiresidue analysis of pesticides

Abundant studies have been published evaluating different parameters of reverse-phase liquid chromatography (LC) and supercritical fluid chromatography (SFC), both coupled to electrospray (ESI)/mass spectrometry (MS) for pesticide residue analysis. However, there is a lack of a comprehensive comparative study that facilitates deep knowledge about the benefits of using each technique. In the present study, the same mass spectrometer was used coupled to both liquid and supercritical fluid chromatographies with a multiresidue method of 215 compounds, for the analysis of pesticide residues in food samples. Through the injection of the spiked extracts, separate experiments were conducted. A study of the optimum ion source temperature using the different chromatography modes was performed. The results were evaluated in terms of sensitivity with tomato, leek, onion, and orange as representative fruit and vegetable matrices. The compounds which reported the highest area values in each chromatography were evaluated through their substance groups and polarity values. The impact of matrix effects obtained in tomato matrix was similar for both cases; however, SFC clearly showed better results in analyzing matrices with a higher number of natural co-extracted compounds. This can be explained by the combination of two effects: (i) chromatography separation and (ii) ion source efficiency. The chromatographic elution presented different profiles of matrix components, which had diverse impact on the coelution with the analytes, being more beneficial when SFC was used in the matrices studied. The data showed that the best results obtained in SFC are also related to a higher ionization efficiency even when the ESI emitter tip was not optimized for SFC flow. In the present study a comprehensive evaluation of the benefits and drawbacks of these chromatography modes for routine pesticide residue analysis related to target compounds/commodities is provided.

Polysaccharide- and β-Cyclodextrin-Based Chiral Selectors for Enantiomer Resolution: Recent Developments and Applications

Polysaccharides, oligosaccharides, and their derivatives, particularly of amylose, cellulose, chitosan, and β-cyclodextrin, are well-known chiral selectors (CSs) of chiral stationary phases (CSPs) in chromatography, because they can separate a wide range of enantiomers. Typically, such CSPs are prepared by physically coating, or chemically immobilizing the polysaccharide and β-cyclodextrin derivatives onto inert silica gel carriers as chromatographic support. Over the past few years, new chiral selectors have been introduced, and progressive methods to prepare CSPs have been exploited. Also, chiral recognition mechanisms, which play a crucial role in the investigation of chiral separations, have been better elucidated. Further insights into the broad functional performance of commercially available chiral column materials and/or the respective newly developed chiral phase materials on enantiomeric separation (ES) have been gained. This review summarizes the recent developments in CSs, CSP preparation, chiral recognition mechanisms, and enantiomeric separation methods, based on polysaccharides and β-cyclodextrins as CSs, with a focus on the years 2019-2020 of this rapidly developing field.

Supercritical fluid chromatography-mass spectrometric determination of chiral fungicides in viticulture-related samples

Supercritical fluid chromatography (SFC), combined with mass spectrometry (MS), was employed for the determination of five chiral fungicides, from two different chemical families (acylalanine and triazol) in wine and vineyard soils. The effect of different SFC parameters (stationary phase, chiral selector, mobile phase modifier and additive) in the resolution between enantiomers and in the efficiency of compounds ionization at the electrospray source (ESI) was thorougly described. Under final working conditions, chiral separations of selected fungicides were achieved using two different SFC-MS methods, with an analysis time of 10 min and resolution factors from 1.05 to 2.45 between enantiomers. In combination with solid-phase extraction and pressurized liquid extraction, they permitted the enantiomeric determination of target compounds in wine and vineyard soils with limits of quantification in the low ppb range (between 0.5 and 2.5 ng mL^-1, and from 1.3 to 6.5 ng g^-1, for wine and soil, respectively), and overall recoveries above 80%, calculated using solvent-based standards. For azolic fungicides (tebuconazole, myclobutanil and penconazole) soil dissipation and transfer from vines to wines were non-enantioselective processes. Data obtained for acylalanine compounds confirmed the application of metalaxyl (MET) to vines as racemate and as the R-enantiomer. The enantiomeric fractions (MET-S/(MET-S+MET-R)) of this fungicide in vineyard soils varied from 0.01 to 0.96; moreover, laboratory degradation experiments showed that the relative dissipation rates of MET enantiomers varied depending on the type of soil.

Recent advances in chiral analysis for biosamples in clinical research and forensic toxicology

This article covers current methods and applications in chiral analysis from 2010 to 2020 for biosamples in clinical research and forensic toxicology. Sample preparation for aqueous and solid biological samples prior to instrumental analysis were discussed in the article. GC, HPLC, capillary electrophoresis and sub/supercritical fluid chromatography provide the efficient tools for chiral drug analysis coupled to fluorescence, UV and MS detectors. The application of chiral analysis is discussed in the article, which involves differentiation between clinical use and drug abuse, pharmacokinetic studies, pharmacology/toxicology evaluations and chiral inversion. Typical chiral analytes, including amphetamines and their analogs, anesthetics, psychotropic drugs, β-blockers and some other chiral compounds, are also reviewed.

Application of chiral chromatography in radiopharmaceutical fields: A review

Chiral column chromatography (CCC) is a revolutionary analytical methodology for the enantioseparation of novel positron emission tomography (PET) tracers in the primary stages of drug development. Due to the different behaviors of tracer enantiomers (e.g. toxicity, metabolism and side effects) in administrated subjects, their separation and purification is a challenging endeavor. Over the last three decades, different commercial chiral columns have been applied for the enantioseparation of PET-radioligand (PET-RL) or radiotracers (PET-RT), using high-performance liquid chromatography (HPLC). The categorization and reviewing of them is a vital topic. This review presents a brief overview of advances, applications, and future prospectives of CCC in radiopharmaceutical approaches. In addition, the effective chromatographic parameters and degravitation trends to enhance enantioseparation resolution are addressed. Moreover, the application and potential of chiral super fluidical chromatography (CSFC) as an alternative for enantioseparation in the field of radiopharmaceutical is discussed. Finally, the crucial application challenges of CCC are explained and imminent tasks are suggested.