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Electron paramagnetic resonance for the detection of electrochemically generated hydroxyl radicals : issues associated with electrochemical oxidation of the spin trap
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Braxton, Emily, Fox, David J., Breeze, Ben G., Tully, Joshua J., Levey, Katherine J., Newton, Mark E. and Macpherson, Julie V. (2022) Electron paramagnetic resonance for the detection of electrochemically generated hydroxyl radicals : issues associated with electrochemical oxidation of the spin trap. Measurement Science Au . doi:10.1021/acsmeasuresciau.2c00049 ISSN 2694-250X. (In Press)
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WRAP-electron-paramagnetic-resonance-hydroxyl radicals-electrochemical-oxidation-spin-trap-Braxton-2022.pdf - Published Version - Requires a PDF viewer. Available under License Creative Commons Attribution 4.0. Download (3031Kb) | Preview |
Official URL: http://dx.doi.org/10.1021/acsmeasuresciau.2c00049
Abstract
For the detection of electrochemically produced hydroxyl radicals (HO·) from the oxidation of water on a boron-doped diamond (BDD) electrode, electron paramagnetic resonance spectroscopy (EPR) in combination with spin trap labels is a popular technique. Here, we show that quantification of the concentration of HO· from water oxidation via spin trap electrochemical (EC)-EPR is problematic. This is primarily due to the spin trap oxidizing at potentials less positive than water, resulting in the same spin trap-OH· adduct as formed from the solution reaction of OH· with the spin trap. We illustrate this through consideration of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin trap for OH·. DMPO oxidation on a BDD electrode in an acidic aqueous solution occurs at a peak current potential of +1.90 V vs SCE; the current for water oxidation starts to rise rapidly at ca. +2.3 V vs SCE. EC-EPR spectra show signatures due to the spin trap adduct (DMPO-OH·) at potentials lower than that predicted thermodynamically (for water/HO·) and in the region for DMPO oxidation. Increasing the potential into the water oxidation region, surprisingly, shows a lower DMPO-OH· concentration than when the potential is in the DMPO oxidation region. This behavior is attributed to further oxidation of DMPO-OH·, production of fouling products on the electrode surface, and bubble formation. Radical scavengers (ethanol) and other spin traps, here N-tert-butyl-α-phenylnitrone, α-(4-pyridyl N-oxide)-N-tert-butylnitrone, and 2-methyl-2-nitrosopropane dimer, also show electrochemical oxidation signals less positive than that of water on a BDD electrode. Such behavior also complicates their use for the intended application.
| Item Type: | Journal Article | |||||||||||||||
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| Subjects: | Q Science > QC Physics Q Science > QD Chemistry |
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| Divisions: | Faculty of Science, Engineering and Medicine > Science > Chemistry Faculty of Science, Engineering and Medicine > Science > Physics |
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| Library of Congress Subject Headings (LCSH): | Electron paramagnetic resonance , Electrochemistry, Hydroxyl group | |||||||||||||||
| Journal or Publication Title: | Measurement Science Au | |||||||||||||||
| Publisher: | American Chemical Society | |||||||||||||||
| ISSN: | 2694-250X | |||||||||||||||
| Official Date: | 2022 | |||||||||||||||
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| DOI: | 10.1021/acsmeasuresciau.2c00049 | |||||||||||||||
| Status: | Peer Reviewed | |||||||||||||||
| Publication Status: | In Press | |||||||||||||||
| Access rights to Published version: | Open Access (Creative Commons) | |||||||||||||||
| Date of first compliant deposit: | 11 October 2022 | |||||||||||||||
| Date of first compliant Open Access: | 11 October 2022 | |||||||||||||||
| RIOXX Funder/Project Grant: |
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