Combined capillary electrophoresis and high performance liquid chromatography studies on the kinetics and mechanism of the hydrogen peroxide–thiocyanate reaction in a weakly alkaline solution

The hydrogen peroxide–thiocyanate reaction has been reinvestigated by means of capillary electrophoresis and high performance liquid chromatography under weakly alkaline conditions at 25.0±0.1 °C. Concentration–time series of thiocyanate, sulfate and cyanate have been followed by capillary electrophoresis as well as that of thiocyanate and hydrogen peroxide by HPLC. It has been clearly demonstrated that OxSCN− (where x=1, 2 and 3) cannot be accumulated in detectable amount in contrast to the results of Christy and Egeberg, hence these species can only be regarded as short-lived intermediates. It has been shown that the overall rate law is first-order with respect to both reactants, but no pH-dependence was observed within the pH range of 8.86–10.08. A simple kinetic model has been proposed to fit all the concentration–time curves simultaneously at five different pHs demonstrating the powerful combination of the experimental techniques CE and HPLC with simultaneous evaluation of kinetic curves. It is also enlightened that the quality of the buffer strongly affects the rate of the overall reaction that increases in the order of application of ammonia, phosphate, carbonate and borate, respectively at a constant ionic strength and pH.