Analytische Chemie
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Among major food contaminants agrochemicals (including insecticides, fungicides and herbicides) are a threat for food safety in many countries. Once they entered the food chain or the environment, the parent compound can be transformed into different products by manmade and natural processes. The transformation products (TPs) might be more toxic and stable than the parent compound. In addition to this the transformation products might undergo conjugation with different compounds and/or changed to phase II metabolites.
Conventional in-vivo or in-vitro methods to study phase I and II metabolism have drawbacks of long-time sample preparation and matrix complexity. Online coupling of an electrochemical cell with liquid chromatography-mass spectrometry (EC–LC–MS) is a promising technique to study metabolites, fate and transformation products of pesticides. The new approach enables to identify metabolic transformation products by oxidizing analyte of interest on the EC, separate the metabolites on HPLC and identifying them by MS.
The aim of the present study is to identify/mimic pesticides phase I metabolites using electrochemical cell coupled to liquid chromatography-mass spectrometry (EC-LC-MS). Metabolic transformed products of two model compounds, fluopyram (fungicide) and chlorpyrifos (insecticide) were studied by EC upfront with MS. The results of EC-LC-MS are compared and discussed with those derived from in-vitro assays and the metabolites identified by LC-MS/MS.
Metabolic transformation products of pesticides by electrochemical cell coupled to LC-MS (EC-LC-MS)
(2016)
Metabolic transformation products (TPs) of the insecticide chlorpyrifos (CPF), the new fungicide fluopyram (FLP) and the broad-spectrum herbicide, glyphosate (GLP), were studied by electrochemistry coupled to mass spectrometry (EC-MS) for the first time. Phase I metabolites of the three pesticides from rat liver in-vitro assay experiments were studied by LC-MS/MS and compared to electrochemically oxidized products from EC-MS.
Known metabolites from S-oxidation, O-dealkylation and hydroxylation of the insecticide chlorpyrifos have been identified by EC-MS and simulated to in-vitro assays. Chlorpyrifos-oxon (CPF-oxon), diethylthiophosphate (DETP), 3,5,6-trichloropiridinol (TCP), diethylphosphate (DEP) and 2,3,5-trichloropyridine (TCPy) were the main EC oxidative TPs and in-vitro assay metabolites of CPF which was also reported by Choe et al.. Fluopyram was extensively converted to a number of electrochemical products including mono- and dihydroxylated derivatives and yet unidentified TPs. Rat liver microsomal assay experiments showed mainly hydroxylated metabolites of FLP which was also reported by the European Food Safety Agency (EFSA). Aminomethyl phosphonic acid (AMPA) was the main TP of glyphosate detected from both EC-MS analysis and in-vitro assay tests.
A number of TPs of CPF, FLP and GLP have been identified by electrochemistry online mass spectrometry and compared to in-vitro assays. Using electrochemistry upfront MS enables fast and matrix free prediction of metabolic pathways, transformation products and/or fate of pesticides. Further studies will focus on structural characterization of detected compounds, phase II metabolites and investigation of real samples.
In particular, the rapid development of lateral flow assays as indispensable tools for everyone to contain the SARS-CoV-2 pandemic has fuelled the global demand for analytical tests that can be used outside dedicated laboratories. In addition to their use in medical diagnostics, rapid tests and assays have become increasingly important in various fields such as food safety, security, forensics, and environmental management. The advantage is obvious: taking the assay directly to the sample minimizes the time between suspicion and decision-making, allowing faster action. Especially today, when mobile communication devices with powerful computing capabilities and built-in cameras are ubiquitous, more people than ever before around the world have the basic skills to operate a powerful detector at their fingertips. This sets the stage for a much wider use of analytical measurements in terms of prognosis and prevention, enabling professional laypersons in particular.
However, current strip-based systems are primarily focused on single parameter analysis, whether it is SARS-CoV-2 biomarkers, blood glucose levels, or lead concentrations in water samples. Industrial applications of such methods also often still rely on single-parameter assays, requiring multiple runs even for a limited number of key parameters. Overcoming these limitations depends on developing low-number multiplexing strategies that ensure robustness, reliability, speed, ease of use, and sensitivity.
This lecture will give an overview of several generic approaches developed in recent years to address these challenges. It will highlight how the synergy of supramolecular (bio)chemistry, luminescence detection, hybrid (nano)materials and device miniaturization can result in powerful (bio)analytical assays that can be used at a point-of-need.1-5 Selected examples will introduce key aspects of such systems that include tailored signaling mechanisms and recognition elements, materials functionalization and device integration, including hybrid nanomaterials, gated indicator release systems, strip modification, and smartphone-based analysis.