Improved Voltammetric Procedure for Chloride Determination in Highly Acidic Media

Cyclic voltammetry can be applied as the reliable method for the determination of chloride ions in a range from several to couple hundred ppm. Since the standard potential of chloride ion/gaseous chlorine is 1.36 V vs NHE the efficient oxidation of Cl- ion occurs at very positive electrode potentials, usually higher than + 1.7 V vs NHE electrode. It is possible to observe this phenomenon only at noble-metal or inert carbon electrodes. Many other solutes, usually organic compounds, are often oxidized at this potential. This is the reason why determination of Cl- content directly from increase of the oxidation current is not reliable and can lead to overestimated values. However, gaseous chlorine, generated at positive potential dissolves in the analyzed solution and can be reduced in the reverse scan of cyclic voltammetric curve. Optimization of the experimental procedure using the statistical tools allowed for the development of the improved method for the direct quantification of chloride ions in acid copper electroplating baths. Under the proposed experimental conditions, the calibration curve (Cl2 voltammetric reduction current vs. chloride ions concentration) is represented by the linear model for the concentration of chlorides ranging from 10 to 200 mg/dm3.