Generation and ESR spin trapping of the cyanide radical. A: Complete system and simulation. 100 mM 14N-DMPO, 10 mM KCN, 1 mg/ml horseradish peroxidase and 350 μM H2O2 were dissolved in 100 mM Chelex-treated phosphate buffer, pH = 7.4, with 25 μM DTPA. To achieve an acceptable signal/noise ratio, the sample was incubated for 15 min (room temperature) and then measured (scan time: 167.77 s). B: As in A, but in the presence of 100 mM 15N-DMPO. C: As in A, but no KCN. D: As in A, but without H2O2. E: As in A, but in the absence of HRP. No significant signals are visible in traces C-E. F: 15N-DMPO in phosphate buffer as used in A. Due to the higher concentration of DMPO and the more sensitive EPR parameters, a slight background signal was detected.