Figure 1: Typical electron spin resonance (ESR) spectra of vitamin C radicals (VCR, ascorbyl radicals) detected in the serum of a healthy subject after DMSO addition. Manganese oxide (MnO) was used as an internal standard. VCR ESR signals were recorded between the third and fourth MnO signals. The intensity of the first VCR signal relative to that of the third MnO signal (VI/MI) was defined as serum VCR.