Detection of the formyl radical by EPR spin-trapping and mass spectrometry.

Abstract

For the first time we here present the unambiguous identification of the formyl radical (•CHO) by EPR (Electron Paramagnetic Resonance) spectroscopy and mass spectrometry (MS) using DMPO (5,5-dimethyl-1-pyrroline N-oxide) as spin trap at ambient temperature without using any catalyst(s). The •CHO was continuously generated by UV photolysis in closed anoxic environment from pure formaldehyde (HCHO) in aqueous solution. The isotropic hyperfine structure constants of •CHO were determined as aN = 15.72G and aH = 21.27G. The signals were deconvoluted and split by simulation in their single adduct components: DMPO-CHO, DMPO-H and DMPO-OH. We verified our results at first using MNP (2-methyl-2-nitroso-propane) as spin trap with known literature data and then mass spectrometry. Similarly the MNP adduct components MNP-CHO, MNP-H as well as its own adduct, the MNP-2-methyl-2-propyl (MNP-MP) were deconvoluted. Due to the low signal intensities, we had to accumulate single measurements for both spin traps. Using MS we got the exact mass of the reduced •CHO adduct independently confirming the result of EPR detection of formyl radical.