Electrocatalytic oxidation of NADH at carbon paste electrodes modified with Meldola Blue adsorbed on zirconium phosphate: effect of Ca2+ and polyethyleneimine

The basic electrochemistry of carbon paste electrodes modified with Meldola Blue adsorbed on zirconium phosphate (MB-ZP-CPEs) and their ability to oxidize NADH have been investigated. Three types of carbon powder (graphite and glassy carbon-type Sigradur K and G) were used to obtain MB-ZP-CPEs. On comparing cyclic voltammograms recorded at MB-ZP-CPEs, similarly prepared from the three different carbon powders, those made with Sigradur K exhibited the lowest background current, and the best MB electrochemistry, seen as the highest peak intensities and smallest peak separation. Using MB-ZP-CPEs based on Sigradur K a study on NADH oxidation was done focusing on the effect of the Ca2+ concentration in the contacting solution and on the addition of polyethyleneimine (PEI) into the paste. It can be stated that MB-ZP-CPEs based on Sigradur K and containing 1.23% (w/w) PEI exhibited the best behavior for NADH oxidation, measured by the highest electrocatalytic rate constant (8.2 x 10(3) M-1 s(-1)).