The electrochemical behaviour of 5-methylphenazonium methylsulphate (PMS) on the solid electrodes in acetonitrile (AN), in dimethylformamide (DMF) and in aqueous buffered solutions, using Britton buffer from pH=1.5 to pH=10.0 is described. In aprotic medium, the PMS reduction involves two quasi-reversible monoelectronic steps, in the potential range from +0.5 V to -1.5 V. During the first step the radical MP. is occurred, in the latter the anion MP-. Considering the HCIO4 addition, for example, in the ratio 1:1 with respect to PMS, in AN, two cathanodic systems are observed: the first at +0.69 V and the second at +0.34 V vs NHE. The protonated forms of the radical and the anion are involved. In DMF, in the same experimental conditions, a single bielectronic step is involved at +0.40 V vs NHE. In aqueous buffered solution, in the range of pH 4-10, a single cathanodic system at +0.15 V vs NHE is observed. Unfortunately, the reduced form of PMS is strongly adsorbed on the electrodic surface. A method of a voltage-facilitated immobilization of PMS on a pyrolytic graphite is shown. At pH=7 the modified electrode catalyzes the electron transfer from NADPH, (NAD)2 or (NADP)2.
Buy this Article