Electrocatalytic Oxidation of NADH in Flow Analysis by Graphite Electrode Modified with 2,6-Dichlorophenolindophenol Salts

Abstract

The preparation of a 2,6-dichlorophenolindophenol (DCPI) modified graphite electrode is described. DCPI was successfully immobilized by physical adsorption onto a plain graphite electrode (DCPI-CME) and onto graphite electrodes pretreated with lanthanum nitrate (DCPI-La-CME) or thorium nitrate (DCPI-Th-CME). The electrochemical behavior of DCPI-CME was extensively studied using cyclic voltammetry. The electrochemical redox reaction of DCPI was found to be fairly reversible at low coverage with E o 0 = þ55 mV (vs. Ag/AgCl/3M KCl) at pH 6.5. A pK a value of 5.8 Ϯ 0.1 for immobilized form of DCPI is determined from the intersection of the lines in the plot E o 0 vs. pH. The current I p has a linear relationship with the scan rate up to 1200 mV s ¹1 , which is indicative for very fast electron transfer kinetics. The calculated value of the standard rate constant is k o = 18 Ϯ 4 s ¹1. No decrease of either the anodic or the cathodic current of the cyclic voltammogram was observed after 500 runs of successive sweeps. The influence of the morphology of the electrode surface on the electrochemical behavior of the DCPI-CME was studied and a mathematical model is proposed, which partly describes the dependence of the geometrical area of the electrode surface on the grid of the emery paper. The modified electrodes were mounted in a flow-injection manifold, poised at þ60 mV (vs. Ag/AgCl/3M KCl) and a catalytic current due to the oxidation of NADH was observed reducing thus the oxidation overpotential of NADH for about 400 mV. Interference from various reductive species present in real samples was investigated. The repeatability was 1.2 % RSD (n = 10 for 0.1 mM NADH). The sensor showed good operational and storage stability.

Novel poly(hexylmethacrylate) composite carbon electrodes modified with Keggin-type tungstophosphate-tetrabutylammonium salts

“…The peak-to-peak separations (DE p ) were 76 mV for the CPE 1 and 170 mV for CPE 2 , indicating quasi-reversible electron transfer processes, the increase for CPE 2 attributed to slower kinetics. As reported previously, the reaction kinetics of electroactive species in concentrated interfacial solution in such systems may be slowed down due to lower mobility of molecules [38].…”

The Importance of Surface Coverage in the Electrochemical Study of Chemically Modified Electrodes

“…The large number of problems associated with the direct electroanalysis of several redox species, namely high overpotential, fouling of the electrode surface, irreversibility and interference of other electroactive species, initiates investigations on redox mediators such as quinones, catechols, redox dyes, metal complexes and conducting organic salts [1±3], which have been successfully used to oxidize a large variety of species such as NADH [4,5], ascorbic acid [6,7], dopamine [8] etc.…”

Amperometric Detection of Periodate Using a Graphite Electrode Modified with a Novel α-Keggin-Type Silicotungstic Acid Salt and Determination of Ethylene Glycol in Antifreeze Fluids

“…The surface coverage G of the modifier and the total effective area of the graphite working electrode were determined with cyclic voltammetry and double step chronocoulometry experiments, respectively [17].…”

“…As it has been documented in previous studies the morphology of the surface of the graphite electrode is very important for the voltammetric and analytical characteristics of the CMEs [17,20]. Polishing with emery paper of grit 1200 had been found to be the most appropriate when mediators with a molecular weight of 326 [17] and 856 [21] daltons have been used.…”

“…Polishing with emery paper of grit 1200 had been found to be the most appropriate when mediators with a molecular weight of 326 [17] and 856 [21] daltons have been used. In this study, three emery papers of grit 500, 800 and 1200 were tested.…”