The hydroxyl radical adduct is characterized by a 1:2:2:1 pat- tern, which arises from the equivalence of the nitrogen and hydrogen hyperfine splitting. The relative intensities could be esti- mated from the peak heights in theDMPO-OHadduct spectra; these intensities indicate the relative concentrations of hydroxyl radi- cal because the EPR spectroscopy signal is directly related to the concentration of spin adducts