Catalytic Voltammetric Determination of Vanadium in Crude Oil at Carbon Nanotube Paste Electrode

A catalytic voltammetric method for the determination of vanadium(V) at a multi-wall carbon nanotube paste electrode (MWCNT-PE) in a 4-(2-pyridylazo)-resorcinol(PAR)-bromate system is proposed. The voltarametric response of V(V)-PAR complex at MWCNT-PE was significantly enhanced because of a catalytic cycle consisting of electrochemical reduction of V(V) ion in the complex and subsequent chemical oxidation of the reduction product of V(V) by bromate. In pH 2.70 H2SO4 solution containing 5.0x10(-6) mol.L-1 PAR and 3.0x10(-2) mol.L-1 KBrO3 without any preconcentration, the linear sweep voltammetric peak current of the catalytic wave was proportional to the vanadium concentration in the range of 8.0x10(-9) to 3.0x10(-6) mol.L-1. The detection limit was 2.5x10(-9) mol.L-1. Using the proposed method, the vanadium concentration in crude oil was evaluated and the results were compared with those of atomic absorption spectrometry.