Simultaneous detection of peracetic acid and hydrogen peroxide by amperometry at Pt and Au electrodes

Based on preliminary voltammetric investigations at both Pt and Au electrodes in aqueous solutions buffered at different pH values in the range 0-10, two possible profitable triple-pulse amperometric approaches were developed for determining simultaneously peroxyacetic acid (PAA) and hydrogen peroxide present in the same samples. At both surfaces a pulsed waveform applied at rotating-disc electrodes was adopted to take advantage on one hand of the optimized signal reproducibility achieved by this potential multistep antifouling approach and on the other hand of the constant thickness of the diffusion layer, which is necessary when the recording of time-independent currents is desired. At a rotating-disc Pt electrode an anodic selective signal was indeed recorded for H2O2 alone, while PAA contents could be inferred only from the difference of convenient signals, since at all pHs explored its sole cathodic reaction could be observed at potentials coincident with those proper for the reduction of H2O2 too. The same pulse approach at Au electrodes instead provided totally independent signals for the two analytes considered, thus proving to be suitable for their independent detection. In fact, H2O2 alone undergoes anodic oxidation also at this surface, while the reduction of PAA occurs at potentials less cathodic than those required for H2O2. At both electrodes, the best results turned out to be achieved at pH 0 in terms of both precision (+/- 2-4%) and detection limits (0.2-0.3 mM), as well as of linear range which extended for about three orders of magnitude. The kinetics of the equilibrium involving the generation of H2O2 from the reaction of PAA with water was also evaluated, since it was suspected of making unreliable the proposed amperometric approaches.