Study of the Electrochemical Behavior of Disperse Blue 1‐Modified Graphite Electrodes. Application to the Flow Determination of NADH

The preparation and the electrochemical study of Disperse Blue 1‐chemically modified electrodes (DB1‐CME), as well as their efficiency for the electrocatalytic oxidation of NADH is described. The proposed mediator was immobilized by physical adsorption onto graphite electrodes. The electrochemical behavior of DB1‐CME was studied with cyclic voltammetry. The electrochemical redox reaction of DB1 was found to be reversible, revealing two well‐shaped pair of peaks with formal potentials 152 and −42 mV, respectively, (vs. Ag/AgCl/3M KCl) at pH 6.5. The current Ip has a linear relationship with the scan rate up to 800 mV s−1, which is indicative for a fast electron transfer kinetics. The dissociation constants of the immobilized DB1 redox couple were calculated pK1=4 and pK2=5. The electrochemical rate constants of the immobilized DB1 were calculated k1°=18 s−1 and k2°=23 s−1 (Γ=2.36 nmol cm−2). The modified electrodes were mounted in a flow injection manifold, poised at +150 mV (vs. Ag/AgCl/3M KCl) and a catalytic current due to the oxidation of NADH was measured. The reproducibility was 1.4% RSD (n=11 for 30 μM NADH) The behavior of the sensor towards different reducing compounds was investigated. The sensor exhibited good operational and storage stability.