Simultaneous evaluation of the dissociated and undissociated acid concentrations by square wave voltammetry using microelectrodes

The square wave voltammetric response of the reduction of acids of different strength namely, hydrochloric acid, phosphoric acid, lactic acid, acetic acid and sodium dihydrogenophosphate at a platinum microdisk electrode are presented. The voltammograms of HCl and H2PO4- display a single peak which height increased linearly with concentration. The acids of intermediary strength exhibit voltammograms resulting from the overlapping of two peaks that are assigned to the reduction of hydrogen ions (H+) and of the undissociated acid form (HA). Peaks separation depends on the acid strength and concentration. A numerical deconvolution of voltammograms was performed based on Gaussian peaks fitting. The deconvoluted peak current data for H+ were validated towards calibration curves of HCl. The validation of the current data of HA was performed using buffer solutions. The methodology present herein allows to assess simultaneously the concentration of each acid form from a single square wave voltammogram.