LC-IRMS Persulfate Oxidation: Case Study on Neonicotinoid-Related Structures

2025 · doi:10.22541/au.173641764.46598868/v1
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Abstract

Rationale: Liquid chromatography-isotope ratio mass spectrometry (LC-IRMS) is used to analyze stable carbon isotope ratios of polar non-volatile compounds. However, challenges with the persulfate-based oxidation interface have been reported, particularly for molecules with recalcitrant structures like those found in neonicotinoids. This study systematically investigates the oxidation efficiency of neonicotinoid-related structures in a commercial LC-IRMS. Methods: : Neonicotinoid proxies of varying molecular complexity were evaluated for carbon recovery and stable carbon isotope ratio accuracy. LC-IRMS parameters such as oxidant concentration, reaction time, temperature, acid concentration, and the presence of AgNO 3 catalyst were varied. Carbon recoveries and δ 13 C biases were determined by injecting an oxidation-independent inorganic carbon standard under identical conditions. Elemental analyzer isotope ratio mass spectrometry (EA-IRMS) was used to normalize δ 13 C values. Results: : Several neonicotinoid derivatives exhibited low carbon recovery and significant δ 13 C bias. Increasing oxidant concentration, reactor temperature, and reaction time improved recoveries but did not fully mitigate isotopic biases. The addition of AgNO 3 improved carbon recoveries for most derivatives but introduced variability in δ 13 C values, likely due to shifts in reaction mechanisms. A workflow to identify oxidation problems during method development was proposed. Conclusions: : Optimization of LC-IRMS oxidation parameters is critical for urea, guanidine, and nitroguanidine derivatives and similar compounds. A systematic evaluation of oxidation efficiencies under different conditions is needed for optimal mineralization and thus more accurate δ 13 C ratios.
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Abstract

Rationale: Liquid chromatography-isotope ratio mass spectrometry (LC-IRMS) is used to analyze stable carbon isotope ratios of polar non-volatile compounds. However, challenges with the persulfate-based oxidation interface have been reported, particularly for molecules with recalcitrant structures like those found in neonicotinoids. This study systematically investigates the oxidation efficiency of neonicotinoid-related structures in a commercial LC-IRMS. Methods: Neonicotinoid proxies of varying molecular complexity were evaluated for carbon recovery and stable carbon isotope ratio accuracy. LC-IRMS parameters such as oxidant concentration, reaction time, temperature, acid concentration, and the presence of AgNO 3 catalyst were varied. Carbon recoveries and δ 13 C biases were determined by injecting an oxidation-independent inorganic carbon standard under identical conditions. Elemental analyzer isotope ratio mass spectrometry (EA-IRMS) was used to normalize δ 13 C values. Results: Several neonicotinoid derivatives exhibited low carbon recovery and significant δ 13 C bias. Increasing oxidant concentration, reactor temperature, and reaction time improved recoveries but did not fully mitigate isotopic biases. The addition of AgNO 3 improved carbon recoveries for most derivatives but introduced variability in δ 13 C values, likely due to shifts in reaction mechanisms. A workflow to identify oxidation problems during method development was proposed. Conclusions: Optimization of LC-IRMS oxidation parameters is critical for urea, guanidine, and nitroguanidine derivatives and similar compounds. A systematic evaluation of oxidation efficiencies under different conditions is needed for optimal mineralization and thus more accurate δ 13 C ratios. Supplementary Material File (20250103-paper-v15.docx) - Download - 1.05 MB Information & Authors Information Version history Peer review timeline Published Rapid Communications in Mass Spectrometry Version of Record12 May 2025Published Copyright This work is licensed under a Non Exclusive No Reuse License. Collection

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Authors Metrics & Citations Metrics Article Usage 262views 174downloads Citations Download citation Felix Niemann, Annika Gruhlke, Maik Jochmann, et al. LC-IRMS Persulfate Oxidation: Case Study on Neonicotinoid-Related Structures. Authorea. 09 January 2025. DOI: https://doi.org/10.22541/au.173641764.46598868/v1 DOI: https://doi.org/10.22541/au.173641764.46598868/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu.

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