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 mug.L-1 level based on differential pulse anodic stripping voltammet ry 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 nitr ic 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 pe ak was split into two signals. The calibration (peak area vs. molybdenum(VI ) concentration) curve was linear over the concentration range of 1.0 x 10( -7) to 1.0 x 10(-6) mol.L (1) and passed through the origin, with a relativ e standard deviation of ca. 4% for 50 mug.L-1 (n = 5). The sensitivity was 8.9 x 10(-2) muA . V . (mug.L-1)(-1). The detection limit (3 sigma) was 2.5 x 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) determina tion severely. The addition of hydrogen peroxide served to prevent interfer ences of titanium(IV) and zirconium(IV). The proposed method was applied to the determination of 4.47 mass% of molybdenum in the high-temperature allo y standard sample (JAERI-R4, Ni71.9 mass%) and was achieved with fairly goo d precision and accuracy within 60 min without any preliminary separation o f the matrix. The method could be applied to the determination of molybdenu m of down to 20 mass ppm in nickel metal provided the deposition potential was changed into -0.9 V vs. SCE.