Voltammetric determination of titanium, vanadium, and molybdenum using a carbon paste electrode modified with cetyltrimethylammonium bromide

Abstract

Methods for the voltammetric determination of titanium, vanadium, and molybdenum using a carbon paste electrode modified in situ with cetyltrimethylammonium bromide (CTAB) are described. Titanium and vanadium are preconcentrated at the electrode surface via their anionic oxalate complexes from acidic solution at −1.2 and −0.9 V vs. the saturated calomel electrode. The accumulation process is due to in situ formation of an ion-exchanger at the electrode surface by adsorption of the surfactant, and to formation of ion-pairs or micellar congregates, since the concentration of CTAB is higher than the critical micellar concentration (CMC). Simultaneously during accumulation, titanium(IV)- and vanadium(V)-oxalates are reduced to their tri- and tetravalent states. The preconcentration of molybdenum(VI) was performed by adsorption and of ion-pairs of cetyltrimethylammonium and Mo(VI)-oxalates at a potential of −0.4 V. Molybdenum(VI)-oxalate is reduced to a mixed-valence compound of Mo(VI) and (V). Linear dependence of current on concentration exists in the ranges of 10 to 250 µg l−1 for titanium, 5 to 200 µg l−1 for vanadium, and 5 to 500 µg l−1 for molybdenum, when applying a preconcentration time of 1 min. The limit of detection (calculated as 3σ) is 0.1 µg l−1 Ti, 0.07 µg l−1 V, and 0.04 µg l−1 Mo with a deposition time of 10 min. The method presented in this report shows that CTAB is a suitable agent for modification of CPEs giving good reproducibility of results.