Dissolved oxygen sensor based on cobalt tetrasulphonated phthalocyanine immobilized in poly- l-lysine film onto glassy carbon electrode

Abstract

A simple and efficient method for determining dissolved oxygen at pH 6.5 is proposed using differential pulse voltammetry (DPV) and chronoamperometry. The sensor was prepared by modifying a glassy carbon (GC) electrode surface with a cobalt tetrasulphonated phthalocyanine (CoTSPc) immobilized in a poly- l-lysine (PLL) film. This sensor showed excellent catalytic activity and stability for oxygen reduction. With this modified electrode the reduction potential of the oxygen was shifted about 200 mV toward less negative value, presenting a peak current much higher than those measured on a bare GC electrode. The linear response range, sensitivity and detection limit obtained were, respectively, 0.2–8.0 mg l −1, 11.0 μA l mg −1 cm −2 and 96 μg l −1 for chronoamperometry and 0.2–8.0 mg l −1, 18.3 μA l mg −1 cm −2 and 72 μg l −1 for DPV. The repeatability and reproductibility of the proposed sensor evaluated in term of relative standard deviation were, respectively, 4.5% and 4.8% for 10 measurements of a 8.0 mg l −1 oxygen solution. The number of electrons involved in oxygen reduction, the heterogenous rate constant ( k) and the diffusion coefficient ( D o) value were evaluated by cyclic voltammetry and with a rotating disk electrode (RDE). These studies showed that two electrons are involved in the oxygen reduction. An average value of the heterogenous rate constant was found to be 4.25 × 10 4 mol −1 l s −1 and the diffusion coefficient was 2.0 × 10 −5 cm 2 s −1.