STEADY-STATE VOLTAMMETRY IN THE PROCESS OF HYDROGEN EVOLUTION IN BUFFER SOLUTIONS

The process of hydrogen evolution occurring at a platinum microelectro de was studied in buffer solutions made by either mono-or polyprotic a cids. Buffers formed either by maxing equal amounts of the weak acid a nd its conjugate base, or an excess of acid or base were considered. T he results demonstrated that the steady state limiting current, I-l, i s related to the amount of both free proton and undissociated acid pre sent in the mixture, even if the pH of the solution is constant or cha nges to a negligible extent. Linear trends, between the steady-state l imiting current and the analytical concentration of the weak acid, C-A , present in the mixture, was found in the buffers, while comparative measurements carried out in solutions containing the weak acids alone, showed that the plots are not linear. Theoretical relationships relat ing I-l and C-A directly were also derived, and they allowed to ration alise the fact that all the buffers formed from a given monoprotic aci d display plots having a common slope, while the buffers obtained from a polyprotic acid may show plots with different slopes. (C) 1998 Else vier Science B.V.