Phenanthroline solution (5 103 mol/L) of 1.5 mL was taken and added with 2.0 mL of phosphate buffer (pH 7.4, 0.05 mol/L), added with 1.0 mL FeSO4 solution (7.5 103 mol/L), evenly mixed immediately, added with 1 mL H2O2 (0.0294 mol/L), and finally supplemented with distilled water to 10 mL.