Electrochemistry coupled online to liquid chromatography-mass spectrometry for fast simulation of biotransformation reactions of the insecticide chlorpyrifos

Identification of transformation products from fluorinated lithium-ion battery additives TPFPB and TPFPP: forever chemicals of tomorrow?

Fluorinated organic compounds (FOCs) represent a class of synthetic chemicals distinguished by their resilient carbon-fluorine bonds, which demonstrate an ability to withstand environmental degradation over an extended period. The integration of FOCs into cutting-edge applications, including lithium-ion batteries (LiBs), presents considerable potential for environmental harm that has not yet been sufficiently addressed. This study focuses on the environmental fate of two fluorinated aromatics, tris(pentafluorophenyl)borane (TPFPB) and tris(pentafluorophenyl)phosphine (TPFPP), given their important role in improving the performance of LiBs. To achieve this, laboratory simulation methods including total oxidizable precursor assay, electrochemistry (EC), Fenton reaction, UV-C irradiation, and hydrolysis were employed. Liquid chromatography and gas chromatography coupled with high-resolution mass spectrometry were used for identification of transformation products (TPs) and prediction of their molecular formulae. Despite the structural similarity between TPFPB and TPFPP, distinct differences in electrochemical behavior and degradation pathways were observed. TPFPB readily underwent hydroxylation and hydrolysis, resulting in a wide range of 49 TPs. A total of 28 TPs were newly identified, including oligomers and highly toxic dioxins. In contrast, TPFPP degraded exclusively under harsh conditions, requiring the development of innovative conditioning protocols for EC. In total, the simulation experiments yielded nine structurally different compounds, including seven previously undescribed, partially defluorinated TPs. This study highlights the potential risks associated with the use of FOCs in LiBs and provides insight into the complex environmental behavior of FOCs.

Online electrochemistry coupling liquid chromatography-mass spectrometry for rapid investigation on the phase I and phase II simulated metabolic reactions of flavonoids

In this study, an online electrochemistry coupling high-performance liquid chromatography-mass spectrometry (EC-HPLC-MS) technology has been developed for simulating metabolic reactions and rapid analysis of metabolites of flavone, quercetin, and rutin, which are not only widely present compounds with pharmacological activity in nature, but also have structural similarity and variability. The simulated metabolic processes of the substrates (phase I and phase II metabolism) were implemented on the surface of glassy carbon electrode (GCE) by using different electrochemical methods. After online chromatographic separation, the products were transmitted to a mass spectrometer for detection, in order to speculate relevant reaction pathways and structural information of the reaction product. The main metabolites, including methylation, hydroxylation, hydrolysis, and conjugation reaction products, had been successfully identified through the designed in situ hyphenated technique. Furthermore, compared with metabolites produced by in vitro incubation of rat liver microsomes, it was found that the products of electrochemical simulated metabolism were more abundant with diverse metabolic pathways. The results indicated that the proposed method exhibited advantages in the sample pretreatment process and detection cycle without compromising the reliability and accuracy of the results.

Sample transformation in online separations: how chemical conversion advances analytical technology

While the advent of modern analytical technology has allowed scientists to determine the complexity of mixtures, it also spurred the demand to understand these sophisticated mixtures better. Chemical transformation can be used to provide insights into properties of complex samples such as degradation pathways or molecular heterogeneity that are otherwise unaccessible. In this article, we explore how sample transformation is exploited across different application fields to empower analytical methods. Transformation mechanisms include molecular-weight reduction, controlled degradation, and derivatization. Both offline and online transformation methods have been explored. The covered studies show that sample transformation facilitates faster reactions (e.g. several hours to minutes), reduces sample complexity, unlocks new sample dimensions (e.g. functional groups), provides correlations between multiple sample dimensions, and improves detectability. The article highlights the state-of-the-art and future prospects, focusing in particular on the characterization of protein and nucleic-acid therapeutics, nanoparticles, synthetic polymers, and small molecules.

An upconversion nanosensor with phenolic-like functionality for accurate identification of chlorpyrifos in grapes

The inappropriate use of the organophosphorus pesticide chlorpyrifos (CPF) in agricultural production could be harmful to the environment and non-target organisms. Here, we prepared a nano-fluorescent probe with phenolic function based on covalently coupled rhodamine derivatives (RDP) of upconverted nano-particles (UCNPs) for trace detection of chlorpyrifos. Due to the fluorescence resonance energy transfer (FRET) effect in the system, the fluorescence of UCNPs is quenched by RDP. The phenolic-functional RDP is converted to the spironolactone form when it captures chlorpyrifos. This structural shift prevents the FRET effect in the system and allows the fluorescence of UCNPs to be restored. In addition, the 980 nm excitement conditions of UCNPs will also avoid interference from non-target fluorescent backgrounds. This work has obvious advantages in terms of selectivity and sensitivity, which can be widely applied to the rapid analysis of chlorpyrifos residues in food samples.

Electrochemistry coupled with mass spectrometry for the prediction of the environmental fate and elucidation of the degradation mechanisms of pesticides: current status and future prospects

One of the crucial steps in the development of a new pesticide (active molecule) is predicting its environmental and in vivo fate, so as to determine potential consequences to a living organism's health and ecology as a whole. In this regard, pesticides undergo transformation processes in response to biotic and abiotic stress. Therefore, there is a need to investigate pesticide transformation products (TPs) and the formation processes they could undergo during the manufacturing process and when discharged into the ecosystem. Although methods based on biological in vitro and in vivo experimental models are tools of choice for the elucidation of metabolic pathways of pesticides (xenobiotics in general), electrochemistry-based techniques offer numerous advantages such as rapid and low-cost analysis, easy implementation, low sample volume requirement, no matrix effects, and miniaturization to improve the performance of the developed methods. However, for greater efficiency, electrochemistry (EC) should be coupled with analytical techniques such as mass spectrometry (MS) and sometimes liquid chromatography (LC), leading to the so-called EC-MS and EC-LC-MS hybrid techniques. In this review, past studies, current applications and utilization of EC-MS and EC-LC-MS techniques for the simulation of environmental fate/degradation of pesticides were reviewed by selected studies with chemical transformation, structures of metabolites, and some experimental conditions. The current challenges and future trends for the mimicry and prediction of the environmental fate/degradation of pesticides based on electrochemical methods combined with mass spectrometry were highlighted.

Versatile Tools for Understanding Electrosynthetic Mechanisms

Electrosynthesis is a popular, green alternative to traditional organic methods. Understanding the mechanisms is not trivial yet is necessary to optimize reaction processes. To this end, a multitude of analytical tools is available to identify and quantitate reaction products and intermediates. The first portion of this review serves as a guide that underscores electrosynthesis fundamentals, including instrumentation, electrode selection, impacts of electrolyte and solvent, cell configuration, and methods of electrosynthesis. Next, the broad base of analytical techniques that aid in mechanism elucidation are covered in detail. These methods are divided into electrochemical, spectroscopic, chromatographic, microscopic, and computational. Technique selection is dependent on predicted reaction pathways and electrogenerated intermediates. Often, a combination of techniques must be utilized to ensure accuracy of the proposed model. To conclude, future prospects that aim to enhance the field are discussed.

Electrochemistry-coupled to liquid chromatography-mass spectrometry-density functional theory as a new tool to mimic the environmental degradation of selected phenylurea herbicides

In vitro and in vivo experimental models, mainly based on cell cultures, animals, healthy humans and clinical trials, are useful approaches for identifying the main metabolic pathways. However, time, cost, and matrix complexity often hinder the success of these methods. In this study, we propose an alternative non-enzymatic method, using electrochemistry (EC) coupled to liquid chromatography (LC) - high resolution mass spectrometry (HRMS) - DFT theoretical calculations (EC/LC-MS/DFT) for the mimicry/simulation of the environmental degradation of phenylurea herbicides, and for the mechanism elucidation of this class of herbicides. Fenuron, monuron, isoproturon, linuron, monolinuron, metoxuron and chlortoluron were selected as relevant model compounds. The intended compounds are oxidized by EC, separated by LC and detected using electrospray ionization HRMS. The main oxidation products were hydroxylated compounds obtained by substitution and addition reactions. Unstable quinone imines/methines, rarely observed by conventional methods, have been identified during the oxidative degradation of phenylurea herbicides for the first time in this study. Some were directly observed and the others were trapped by glutathione GSH. Reactions such as hydrolytic substitutions (-Cl/+OH and -C₃H₇/+OH and -CH₃/+OH and -OCH₃/+OH), aromatic hydroxylation, alkyl carbon hydroxylation, dehydrochlorination/dehydromethylation/dehydromethoxylation and conjugation have been successfully mimicked. The obtained results, supported by theoretical calculations, are useful for simulating/understanding and predicting the oxidative degradation pathways of pesticides in the environment.

Analysis of Food by High Performance Liquid Chromatography Coupled with Coulometric Detection and Related Techniques: A Review

The development of single coulometric cells in combination with high performance liquid chromatography to dual cells and to the coulometric electrode array detector is described. An overview is given about the application of these methods in food chemistry. Easily oxidizable compounds, such as phenolic substances, pesticides, or vitamins, can be determined, as well as substances with high oxidation potentials or electroinactive compounds. Substances exhibiting poor electrochemical activity can be transformed to electroactive compounds by precolumn derivatization, postcolumn photochemical reactions, postcolumn enzyme reactors, or by using the oxidative/reductive mode for coulometric electrode array detection. Furthermore, it is shown that the interesting combination of high performance liquid chromatography with electrochemistry and mass spectrometry has opened further possibilities with respect to interpretation of redox reactions, drug metabolism studies, metabolomics, and electrochemical derivatization.

Glucosylation and Glutathione Conjugation of Chlorpyrifos and Fluopyram Metabolites Using Electrochemistry/Mass Spectrometry

Xenobiotics and their reactive metabolites are conjugated with native biomolecules such as glutathione and glucoside during phase II metabolism. Toxic metabolites are usually detoxified during this step. On the other hand, these reactive species have a potential health impact by disrupting many enzymatic functions. Thus, it is crucial to understand phase II conjugation reactions of xenobiotics in order to address their fate and possible toxicity mechanisms. Additionally, conventional methods (in vivo and in vitro) have limitation due to matrix complexity and time-consuming. Hence, developing fast and matrix-free alternative method is highly demandable. In this work, oxidative phase I metabolites and reactive species of chlorpyrifos (insecticide) and fluopyram (fungicide) were electrochemically produced by using a boron-doped diamond electrode coupled online to electrospray mass spectrometry (ESI-MS). Reactive species of the substrates were trapped by biomolecules (glutathione and glucoside) and phase II conjugative metabolites were identified using liquid chromatography (LC)-MS/MS, and/or Triple time of flight (TripleTOF)-MS. Glutathione conjugates and glucosylation of chlorpyrifos, trichloropyridinol, oxon, and monohydroxyl fluopyram were identified successfully. Glutathione and glucoside were conjugated with chlorpyrifos, trichloropyridinol, and oxon by losing a neutral HCl. In the case of fluopyram, its monohydroxyl metabolite was actively conjugated with both glutathione and glucoside. In summary, seven bioconjugates of CPF and its metabolites and two bioconjugates of fluopyram metabolites were identified using electrochemistry (EC)/MS for the first time in this work. The work could be used as an alternative approach to identify glutathione and glucosylation conjugation reactions of other organic compounds too. It is important, especially to predict phase II conjugation within a short time and matrix-free environment.

Transformation Products of Organic Contaminants and Residues-Overview of Current Simulation Methods

The formation of transformation products (TPs) from contaminants and residues is becoming an increasing focus of scientific community. All organic compounds can form different TPs, thus demonstrating the complexity and interdisciplinarity of this topic. The properties of TPs could stand in relation to the unchanged substance or be more harmful and persistent. To get important information about the generated TPs, methods are needed to simulate natural and manmade transformation processes. Current tools are based on metabolism studies, photochemical methods, electrochemical methods, and Fenton’s reagent. Finally, most transformation processes are based on redox reactions. This review aims to compare these methods for structurally different compounds. The groups of pesticides, pharmaceuticals, brominated flame retardants, and mycotoxins were selected as important residues/contaminants relating to their worldwide occurrence and impact to health, food, and environmental safety issues. Thus, there is an increasing need for investigation of transformation processes and identification of TPs by fast and reliable methods.

Preparing the key metabolite of Z-ligustilide in vivo by a specific electrochemical reaction

The key in vivo metabolites of a drug play an important role in its efficacy and toxicity. However, due to the low content and instability of these metabolites, they are hard to obtain through in vivo methods. Electrochemical reactions can be an efficient alternative to biotransformation in vivo for the preparation of metabolites. Accordingly, in this study, the metabolism of Z-ligustilide was investigated in vitro by electrochemistry coupled online to mass spectrometry. This work showed that five oxidation products of the electrochemical reaction were detected and that two of the oxidation products (senkyunolide I and senkyunolide H) were identified from liver microsomal incubation as well. Furthermore, after intragastric administration of Z-ligustilide in rats, senkyunolide I and senkyunolide H were detected in the rat plasma and liver, while 6,7-epoxyligustilide, a key intermediate metabolite of Z-ligustilide, was difficult to detect in vivo. By contrast, 6,7-epoxyligustilide was obtained from the electrochemical reaction. In addition, for the first time, 6 mg of 6,7-epoxyligustilide was prepared from 120 mg of Z-ligustilide. Therefore, electrochemical reactions represent an efficient laboratory method for preparing key drug metabolites.

Prediction of biotransformation products of the fungicide fluopyram by electrochemistry coupled online to liquid chromatography-mass spectrometry and comparison with in vitro microsomal assays

Biotransformation processes of fluopyram (FLP), a new succinate dehydrogenase inhibitor (SDHI) fungicide, were investigated by electrochemistry (EC) coupled online to liquid chromatography (LC) and electrospray mass spectrometry (ESI-MS). Oxidative phase I metabolite production was achieved using an electrochemical flow-through cell equipped with a boron-doped diamond (BDD) electrode. Structural elucidation and prediction of oxidative metabolism pathways were assured by retention time, isotopic patterns, fragmentation, and accurate mass measurements using EC/LC/MS, LC-MS/MS, and/or high-resolution mass spectrometry (HRMS). The results obtained by EC were compared with conventional in vitro studies by incubating FLP with rat and human liver microsomes (RLM, HLM). Known phase I metabolites of FLP (benzamide, benzoic acid, 7-hydroxyl, 8-hydroxyl, 7,8-dihydroxyl FLP, lactam FLP, pyridyl acetic acid, and Z/E-olefin FLP) were successfully simulated by EC/LC/MS. New metabolites including an imide, hydroxyl lactam, and 7-hydroxyl pyridyl acetic acid oxidative metabolites were predicted for the first time in our study using EC/LC/MS and liver microsomes. We found oxidation by dechlorination to be one of the major metabolism mechanisms of FLP. Thus, our results revealed that EC/LC/MS-based metabolic elucidation was more advantageous on time and cost of analysis and enabled matrix-free detection with valuable information about the mechanisms and intermediates of metabolism processes. Graphical abstract Oxidative metabolism of fluopyram.

Instrumentation and applications of electrochemistry coupled to mass spectrometry for studying xenobiotic metabolism: A review

The knowledge of metabolic pathways and biotransformation of xenobiotics, artificial substances foreign to the entire biological system, is crucial for elucidation of degradation routes of potentially toxic substances. Nowadays, there are many methods to simulate xenobiotic metabolism in the human body in vitro. In this review, the metabolism of various substances in the human body is described, followed by a summary of methods used for prediction of metabolic pathways and biotransformation. Above all, focus is placed on the coupling of electrochemistry to mass spectrometry, which is still a relatively new technique. This promising tool can mimic both oxidative phase I and conjugative phase II metabolism. Different experimental arrangements, with or without a separation step, and various applications of this technique are illustrated and critically reviewed.