Radical identification by liquid chromatography/thermospray mass spectrometry

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Abstract
Radical adducts of 5,5‐dimethyl‐1‐pyrroline N‐oxide (DMPO) with hydroxyl, methanol‐derived, and ethanol‐derived radicals were detected by a combination of liquid chromatography with either electron paramagnetic resonance or thermospray mass spectrometry (LC/EPR or LC/TSP‐MS) in the Fenton system (with methanol or ethanol). One radical adduct was observed in the reaction of DMPO with the hydroxyl radical or the methanol‐derived radical, while two adducts were detected in the reaction of DMPO with ethanol‐derived radicals. The LC/TSP‐MS spectra showed quasi‐molecular ions [M+H]+ at m/z 146 and m/z 160 for the methanol‐derived and ethanol‐derived radical adducts, respectively, and an apparent molecular ion M+ at m/z 130 for the hydroxyl radical adduct. Use of methyl‐D3 alcohol (CD3OH) and ethyl‐D5 alcohol (CD3CD2OH) indicated that carbon‐centered radicals are formed. Experiments with partially deuterated ethanol (CD3CH2OH and CH3CD2OH) indicated that the two adducts observed in the reaction of DMPO with ethanol‐derived radicals correspond to the two diastereomeric adducts of DMPO with the α‐hydroxyethyl free radical.

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