ULTRATRACE MEASUREMENTS OF SELENIUM BY CATHODIC STRIPPING VOLTAMMETRY IN THE PRESENCE OF RHODIUM

A remarkably sensitive cathodic stripping voltammetric procedure for ultratrace measurements of selenium in the presence Of added rhodium is described. The method is based on the accumulation and subsequent reduction of a Rh2Se3 layer on the hanging mercury drop electrode. Optimum experimental conditions were established, including the use of a 0.1 M sulfuric acid solution containing 10 mug l-1 rhodium, and preconcentration at -0.2 V followed by a fast linear scan. Such conditions yield an extremely low detection limit of 0.5 ng l-1 (6 x 10(-12) M) selenium following a 3-min preconcentration. The improved sensitivity (over earlier cathodic stripping voltammetric schemes) is coupled to high selectivity and precision. Applicability to assays of groundwater and river water samples is illustrated.