Fast and highly sensitive method for molybdenum(VI) determination by catalytic adsorptive stripping voltammetry

The determination of Mo(VI) in water samples by electroanalytical techniques has been studied previously. Special attention has been paid to catalytic adsorptive stripping voltammetry (cAdSV) due to the high sensitivity and low detection limits achieved with this technique. In this work, a fast and sensitive method was optimized and developed for Mo(VI) determination by cAdSV. The method is based on the accumulation of the Mo(VI) complex with 5-chloro-7-iodo-8-hydroxyquinoline (Clioquinol, CQ) and its reduction on the electrode surface in the presence of KBrO3. An increase of the intensity of the reduction signal of the complex in the presence of potassium bromate was observed (catalytic effect). The effects of different experimental conditions on the signal response were studied. These were optimized to obtain the highest sensitivity. The optimal conditions were pH: 4.4 (acetate buffer), potassium bromate concentration (CKBrO3): 1.8 × 10−2 mol L−1, CQ concentration (CCQ): 1.5 × 10−5 mol L−1, accumulation potential (Eacc): −0.10 V and accumulation time (tacc): 10 s. Under the optimal conditions, the repeatability was 5.4% (RSD) for 20 successive assays with a 200 ng L−1 solution of Mo(VI). The detection limit (DL) was 3.1 ng L−1, the quantification limit (QL) was 10.3 ng L−1 and linearity was maintained up to 580.0 ng L−1. Studies of the interference were made for 29 foreign metal ions in the presence of 1,2−cyclohexylenedinitrilo tetraacetic acid (CDTA) and fluoride ion as masking agents. The accuracy of the methodology was evaluated using three different water certified reference materials with different Mo(VI) concentrations and matrix compositions. The method was applied to the determination of Mo(VI) in tap water, river water from a mining zone in the north of Chile and purified bottled water with satisfactory results.