SYNTHESIS OF COBALTOCENIUM SALTS FOR USE AS REDOX LABELS AND THEIR INCORPORATION INTO NAFION FILMS

A cobaltocenium label was covalently attached to two antidepressants, nortriptyline and desipramine, via an amide linkage, and also to the h ydrazine derivative of the biologically important compound biotin (vit amin H), again via an amide linkage. Analytically pure samples of thes e new cobaltocenium salts could be obtained by chromatography on silic a gel followed by elution with aqueous acetone solutions containing so dium chloride (NaCl). These positively charged cobaltocenium ions prec oncentrate in a polyanionic Nafion film coated on a glassy carbon surf ace, albeit at different concentration levels. One factor which seems to influence the amount of cobaltocenium ion that enters the film is p olarity since the cobaltocenium ion containing the rather polar biotin preconcentrates at the lowest level in the relatively hydrophobic Naf ion. Square-wave voltammograms of Nafion films containing these cobalt ocenium cations exhibit a one-electron, reversible, reduction wave at approximately -1.1 V (vs Ag/AgCl) with peak currents that are sufficie ntly large to permit detection of 10(-8) m quantities of these substan ces in the bulk solution.