Determination of silver ions at submicrogram-per-liter levels using anodic square-wave stripping voltammetry

Square-wave stripping voltammetry at a carbon paste electrode was used to develop a method to measure silver ions at concentrations as low as 0.2 μg/L in surface waters. Sample matrix was found to be an important factor affecting the measurement results. Because of these matrix effects, the peak shape of the voltammograms varied, and multiple stripping peaks for silver were observed. Total charge provided a more reliable measure of deposited silver than did peak height. The precision of the method for the analysis of standard reference materials containing silver was estimated to be 7.2% relative SD at 1 SD using a 95% confidence interval of the individuals. A full factorial experiment was performed to determine how the following factors affected measurement variability: electrode, renewal of the carbon paste electrode surface, silver ion concentration, preparation of standards and samples, and day-to-day variability. Samples of lake and river water were collected and analyzed for silver ion. In all samples the measured concentration of silver ion was <0.2 μg/L, whereas the concentration of total silver was typically >0.5 μg/L. Spiking experiments showed that the constituents of the river water samples had a greater ability to bind (remove) silver ion than did the lake water.