Trace determination of molybdenum by anodic adsorptive stripping voltammetry using a multi-walled carbon nanotubes modified carbon paste electrode

A method for the voltammetric determination of trace molybdenum using a multi-walled carbon nanotubes modified carbon paste electrode (MWCNT/CPE) was described. The new procedure is based on the adsorptive accumulation of the Mo(VI)–alizarin violet (AV) complex onto the surface of the modified electrode, followed by the electrochemical oxidation of adsorbed species. The modified electrode showed high electrocatalytic activity toward the oxidation of the free ligand and the complex and the peak current was enhanced significantly. The optimal experimental conditions include the use of 0.12 mol L−1 potassium biphthalate (KHP) buffer (pH 3.6), 4.0 × 10−6 mol L−1 AV (cMo(VI) ≤ 1.0 × 10−7 mol L−1)/4.0 × 10−5 mol L−1AV (cMo(VI) > 1.0 × 10−7 mol L−1), an accumulation potential of −0.30 V (versus SCE), an accumulation time of 120 s, a scan rate of 100 mV s−1 and a second-order derivative linear scan mode. The oxidation peak for the complex appears at 0.59 V. The peak current increases linearly with Mo(VI) concentration in the range of 4.0 × 10−10 mol L−1 to 1.0 × 10−7 mol L−1 and 2.0 × 10−7 mol L−1 to 8.0 × 10−6 mol L−1 and the detection limit (S/N = 3) is 1.0 × 10−10 mol L−1 (accumulation time 120 s). The proposed method was applied to the determination of Mo(VI) in natural water samples with satisfactory results.