ABSTRACT
Because the disulfide of cystine was oxidized, the study of cystine was extended to the determination of insulin, which is a protein that contains two peptide chains that are linked by disulfides. The bovine insulin that was used had a molecular weight of 5733 Da and three disulfide bonds. Evidence for the oxidation of insulin at pH 2.0 at a mvRuOxcoated electrode was obtained by flowinjection analysis with amperometric detection [10]. Initially, a HDV (Figure 3) was developed. As described above, HDV provides current-potential information at concentrations lower than those suited to conventional cyclic voltammetry because of a higher signal-to-background ratio. Under the conditions in Figure 3 with 0.96 V versus Ag/AgCl as the applied potential, the figures-of-merit in Table 1 were obtained. As shown in Figure 4, the oxidation of 95 nM bovine insulin (7.5 µL injection) yielded a signal well above the baseline. The tabulated detection limited was calculated from results represented in Figure 4.
