Differential Pulse Anodic Stripping Voltammetry of Molybdenum(VI) at Glassy Carbon Disk Electrode

A simple and rapid method is described for the determination of molybdenum(VI) at μg·L−1 level based on differential pulse anodic stripping voltammetry at a glassy carbon disk electrode without adding any complexing agents. Octamolybdate formed in a 0.05 mol·L−1 hydrochloric acid −0.05 mol·L−1 nitric acid mixture solution (4 mL) at pH 3 in the presence of 10 vol% acetone was electrodeposited on the working electrode at −1.2 V vs. SCE for 10 min, and the deposits were then stripped in another solution (the acid mixture solution in the absence of acetone) at a scan rate of 50 mV·s−1 to 0.2 V vs. SCE. A quantitative and reproducible peak was obtained, although the peak was split into two signals. The calibration (peak area vs. molybdenum(VI) concentration) curve was linear over the concentration range of 1.0×10−7 to 1.0×10−6 mol·L−1 and passed through the origin, with a relative standard deviation of ca. 4% for 50 μg·L−1 (n=5). The sensitivity was 8.9×10−2 μA·V·(μg·L−1)−1. The detection limit (3σ) was 2.5×10−8 mol·L−1 using a deposition time of 10 min. Tantalum(V), tungsten(VI), vanadium(V) and phosphate interfered with the molybdenum(VI) determination severely. The addition of hydrogen peroxide served to prevent interferences of titanium(IV) and zirconium(IV). The proposed method was applied to the determination of 4.47 mass% of molybdenum in the high-temperature alloy standard sample (JAERI-R4, Ni71.9 mass%) and was achieved with fairly good precision and accuracy within 60 min without any preliminary separation of the matrix. The method could be applied to the determination of molybdenum of down to 20 mass ppm in nickel metal provided the deposition potential was changed into −0.9 V vs. SCE.