High-accuracy differential-pulse anodic stripping voltammetry with indium as an internal standard

Indium(III) is used as an internal standard for the determination of cadmium, copper and lead at the 20 ng g−1 level by using differential-pulse anodic stripping voltammetry; the supporting electrolyte is 1.0 mol l−1 ammonium bromide/0.25 mol l−1 nitric acid. For each solution, each stripping peak of interest is normalized to the corresponding peak height obtained in the same voltammogram for a known, added concentration of indium(III). A calibration curve is prepared for each element by using these normalized peak heights. The technique is demonstrated for NBS SRM 1643b (Trace Elements in Water). The relative standard deviations for six independent determinations of Cd, Cu, and Pb at the 20 ng g−1 level are 1.9%, 5.4%, and 1.2%, respectively. The imprecision for copper is limited by the sloping baseline at its stripping potential. The detection limit for each element is less than 1 ng g−1.