Adsorptive stripping voltammetry determination of molybdenum(VI) in water and soil

A differential pulse stripping voltammetry method for the trace determination of molybdenum(VI) in water and soil has been developed. In 0.048M oxalic acid and 6 x 10(-5)M Toluidine Blue (pH 1.8) solution, Mo(V), the reduction product of Mo(VI) in the sample solution, can form a ternary complex, which can be concentrated by adsorption on a static mercury drop electrode at -0.1 V (vs. Ag/AgCl). The adsorbed complex gives a well-defined cathodic stripping current peak at -0.30 V, which can be used for determining Mo(VI) in the range 5 x 10(-10)-7 x 10(-9)M, with a detection limit of 1 x 10(-10)M (4 min accumulation). The method is also selective. Most of the common ions do not interfere but Sn(IV) and large amounts of Cu(2+), Ag(+) and Au(3+) affect the determination.