Electrochemical properties and electrocatalytic activity of hematoxylin modified carbon paste electrode toward the oxidation of reduced nicotinamide adenine dinucleotide (NADH)

The electrocatalytic oxidation of nicotinamide adenine dinucleotide (NADH) was studied on a hematoxylin modified carbon paste electrode (HMCPE), using cyclic voltammetry, chronoamperometry and differential pulse voltammetry as diagnostic techniques. The surface charge transfer rate constant, ks, and the charge transfer coefficient, αc, for electron transfer between the CPE and the spiked hematoxylin were estimated as 89.56 ± 0.75 s−1 and 0.52, respectively, in pH 7.0, according to the procedure of Laviron. The cyclic voltammograms of the modified electrode indicated that the reactivity of spiked hematoxylin was strongly dependent on the solution pH. Two linear segments were found with slope values of −59.0 and −28.3 mV/pH in the ranges of pH 2.0–8.0 and 8.0–10.0, respectively. The hematoxylin modified electrode showed excellent electrocatalytic activity toward NADH oxidation in a phosphate buffer solution (pH 7.0) with a diminution of the overpotential of about 280 mV, compared to the process at an unmodified electrode. The electron transfer coefficient, αc, and the heterogeneous rate constant, kh, for oxidation of NADH at the hematoxylin modified electrode were also determined as 0.22 and 2.15 × 10−3 cm s−1, respectively, by cyclic voltammetry measurements. Differential pulse voltammetry (DPV) exhibited a wide linear dynamic ranges and a lower detection limit of 0.08 μM for NADH.