Determination of molybdenum in the presence of 2-(2-benzothiazolylazo)-p-cresol by catalytic-adsorptive stripping voltammetry

The adsorptive collection of the molybdenum (VI) complexed with 2-(2-benzothiazolylazo)-p-cresol (BTAC) coupled with the catalytic current of the adsorbed complex at a static mercury drop electrode yields an ultrasensitive voltammetric procedure for the determination of molybdenum. Optimal experimental conditions were: a stirred acetate buffer ¶0.2 M (pH 3.5) as supporting electrolyte, a BTAC concentration of 1.0 × 10^–6 M as ligand, and a concentration of 0.1 M potassium nitrate as the oxidizing agent. In addition, a preconcentration potential of –0.080 V vs Ag/AgCl (3 M KCl), equilibration time of 15 s, a frequency of 30 Hz, a scan increment of 2 mV, a pulse amplitude of 0.050 mV, and a drop area of 0.032 cm² were used. The cyclic voltammogram was recorded using a staircase wave with a scan rate of 100 mV/s. The forward scan starts at the initial potential of –0.080 V and is reversed at –0.90 V. Using the catalytic current at ～–0.55 V the response to the Mo(VI) was found to be linear over a concentration range of 1.0–10.0 μg/L. The limit of detection is as low as 6.2 × 10^–10 M with 4 min of preconcentration time. The possible interference of other trace ions was investigated. The merits of this procedure are demonstrated using of reference samples.