Chemische Charakterisierung und Spurenanalytik
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The knowledge of transformation pathways and identification of transformation products (TPs) of veterinary drugs is important for health, food and environmental matters. Monensin (MON) is an ionophore antibiotic widely used to cure and prevent coccidiosis by chicken especially in broiler farming. Residues can be found in food products (chicken and eggs) and in the environment (manure, soil, water). Several transformation processes can alter the parent compound MON, ranging from biotransformation in living organism to biotic/abiotic and microbial processes in environmental matters.
The main objective of this work was to investigate the potential of electrochemistry (EC) to simulate oxidative transformation processes of MON and to predict TPs. An electrochemical reactor was used consisting of a flow-through cell with a glassy carbon working electrode. Derived TPs were analyzed by online coupling of EC and high-resolution mass spectrometry (HRMS) and LC/HRMS offline measurements. Among the generated TPs already known as well as unknown TPs of MON could be found.
Additionally, MON was subjected also to other transformation experiments like metabolism tests with rat microsomes or the pH-dependent hydrolysis. As a result, different targeted and suspected TPs could be identified by analysis with LC/HRMS.
An overview of detected/identified TPs from this study will be presented in comparison to literature known metabolites and TPs.
Online coupling of electrochemistry with mass spectrometry (EC/MS) is highly promising for prediction and simulation of metabolic processes of xenobiotics in living organisms. Less time and cost of analysis, matrix free detection, and automation make EC/MS-based metabolomics superior over traditional in-vivo and in-vitro methods. Furthermore, EC/MS has a special feature to identify reactive intermediates and reaction mechanisms.
The main objective of this work was to simulate biotransformation processes of pesticides by EC/MS and to elucidate the Transformation products (TPs). We have studied the oxidative phase I metabolism processes of selected pesticides by EC/MS or with liquid chromatography (EC/LC/MS) and compared the derived TPs with cytochrome based metabolites. The electrochemical TPs were produced by boron-doped diamond electrode, separated by LC, and detected by single quadrupole ESI-MS online. Structural identification of both electrochemical oxidation and liver microsome metabolites were based on accurate mass measurements by FT-ICR high-resolution mass spectrometry, isotopic pattern, MS/MS fragmentation, and Retention time alignments.
Main phase I oxidative metabolites by P-oxidation, N- & O- dealkylation, dechlorination, hydroxylation, and -OH- oxidation have been identified. Many targeted and untargeted metabolites have been identified by EC/(LC)/MS. Additionally, reactive species have been trapped online by biomolecules to study phase II conjugative reactions. Furthermore, we synthesized TP standards by EC/MS and applied them for pesticide's TPs occurrence investigation in foodstuf matrices.