Anodic stripping voltammetry of inorganic species of As³⁺ and As⁵⁺ at gold-modified boron doped diamond electrodes

Electrochemical detection of mixture solutions of As³⁺ and As⁵⁺ has been investigated by stripping voltammetry at gold-modified diamond electrodes. The method was performed based on stripping oxidation of As⁰ deposited at the electrode surface. Whereas As³⁺ can be deposited by simple electrochemical reduction of As³⁺ to As⁰ at -0.4 V (vs. Ag/AgCl), much higher potential is required to overcome the activation energy of As⁵⁺ reduction. However, in such a high potential, hydrogen evolution also occurs. Consequently, one more step should be added to release the hydrogen gas adsorbed at the electrode surface during the reduction step. During the deposition of As⁵⁺, As³⁺ species was also simultaneously deposited. Therefore, to differentiate As³⁺ and As⁵⁺ quantification in a mixture solution, both stripping voltammetry methods should be performed and calculated mathematically. Comparison of stripping voltammograms of both methods for As³⁺ solution in the absence of As⁵⁺ demonstrated similar peak shapes and current intensities, confirming that error calculation of As⁵⁺ concentration in the mixture solution with As³⁺ can be avoided. Good linear responses were observed for each standard solution of As³⁺ and As⁵⁺. Linear calibration curve could also be achieved for a series concentrations of 100-1000 ppb As⁵⁺ in a mixture solution with 100 ppb As³⁺ (r² = 0.99) and for a series concentrations of 5-30 ppb As³⁺ in a mixture solution with 100 ppb As⁵⁺. Detection limits of 5 and 100 ppb can be achieved for As³⁺ and As⁵⁺ in a mixture solution, respectively. The reproducibility was shown for stripping voltammetry of As³⁺ and As⁵⁺ with an RSD (n = 8) of 7.5% and 8.4%, respectively. Good stability of gold-modified diamond electrodes before and after arsenic detection was also evaluated by SEM image. Application of the method for real sample analysis was performed for arsenic detection in Yokohama tap water.