Hydrolysis and oxidation of formamidine disulfide in acidic medium were investigated using high-performance liquid chromatography(HPLC) and mass spectrometry(MS) at 25 °C.By controlling the slow reaction rate and choosing appropriate mobile phase,HPLC provides the unique advantages over other methods(UV-Vis,chemical separation) in species tracking and kinetic study.In addition to thiourea and formamidine sulfinic acid,two unreported products were also detected in the hydrolysis reaction.Mass spectrometry measurement indicates these two products to be formamidine sulfenic acid and thiocyanogen with mass weights of 92.28 and 116.36,respectively.In the oxidation of formamidine disulfide by hydrogen peroxide,besides thiourea,formamidine sulfenic acid,formamidine sulfinic acid,thiocyanogen and urea,formamidine sulfonic acid and sulfate could be detected.The oxidation reaction was found to be first order in both formamidine disulfide and hydrogen peroxide.The rate constants of hydrolysis and oxidation reactions were determined in the pH range of 1.5-3.0.It was found both rate constants are increased with the increasing of pH.Experimental curves of different species can be effectively simulated via a mechanism scheme for formamidine disulfide oxidation,including hydrolysis equilibrium of formamidine disulfide and irreversible hydrolysis of formamidine sulfenic acid. Hydrolysis and oxidation of formamidine disulfide in acidic medium were investigated using high-performance liquid chromatography (HPLC) and mass spectrometry (MS) at 25 ° C.By controlling the slow reaction rate and choosing appropriate mobile phase, HPLC provides the unique advantages over other Methods (UV-Vis, chemical separation) in species tracking and kinetic study. addition to thiourea and formamidine sulfinic acid, two unreported products were also detected in the hydrolysis reaction. Mass spectrometry measurement indicates these two products to be formamidine sulfenic acid and thiocyanogen with mass weights of 92.28 and 116.36, respectively. In the oxidation of formamidine disulfide by hydrogen peroxide, besides thiourea, formamidine sulfenic acid, formamidine sulfinic acid, thiocyanogen and urea, formamidine sulfonic acid and sulfate could be detected. be first order in both formamidine disulfide and hydrogen peroxide. rate-of-constants of hydrolysis an d oxidation reactions were determined in the pH range of 1.5-3.0. It was found both rate constants are increased with the increasing of pH. Experimental cycles of different species can be effectively simulated via a mechanism scheme for formamidine disulfide oxidation, including hydrolysis equilibrium of formamidine disulfide and irreversible hydrolysis of formamidine sulfenic acid.