POLISHABLE COMPOSITE ELECTRODE BASED UPON GRAPHITE POWDER MODIFIED WITH AN ELECTROCHEMICALLY DEPOSITED CATALYST

A polishable bulk-modified electrode is described that contains polymeric-mixed valent. ruthenium oxide with cyano cross-links (mvRuCN) as a catalyst. Because mvRuCN is not available as an isolated compound, it was electropolymerized on graphite powder that was subsequently formed into a conducting composite with epoxy. Except for promoting oxidations at a more positive potential, this composite behaved the same as mvRuCN films on glassy carbon. Electrocatalytic oxidation of various N-nitrosamines, As(III) glutathione, isotocin, and myoglobin was observed. Flow-injection analysis of 50 mu M N-nitrosodi-n-propylamine with amperometric detection at the bulk-modified composite electrode yielded currents of 2.5 +/- 0.1 mu A (5 trials) when the carrier solution is pH 1.5 phosphate buffer. The use of-a micellar carrier, pH 1.5 phosphate buffer in 0.01 M hexadecyltrimethylammonium chloride, decreased the sensitivity of the flow-injection amperometric determination of N-nitrosodi-n-phenylamine by 50%, but otherwise, the behavior of the electrode was unchanged. The major advantages of the bulk-modified electrode over the surface-modified electrode was the long-term stability (at least several months with dry storage) and polishability. Regarding the latter, 19 replicates of the oxidation of As(III) yielded a relative standard deviation (RSD) of the current response of 3% when the surface was polished between each trial.