Electrocatalytic detection of streptomycin and related antibiotics at ruthenium dioxide modified graphite-epoxy composite electrodes

Abstract

The application of ruthenium dioxide (RuO₂) modified electrodes to the electrocatalytic detection of the saccharide-related antibiotics streptomycin, novobiocin and neomycin, at low fixed potentials, was investigated. The RuO₂-modified graphite-epoxy composite electrodes give extremely stable and reproducible catalytic oxidation currents for these antibiotics at potentials as low as +0.2 V (versus Ag-AgCl). Rapid quantification at the micromolar level is therefore possible. Standard calibration graphs for streptomycin and neomycin yielded slopes of 4.43 and 0.08 nA µM^–1 over the linear ranges of 1.5 × 10^–6–2.5 × 10^–4 and 1 × 10^–5–2 × 10^–3M, respectively. Owing to its catalytic oxidation by the Ru^III-Ru^IV couple, rather than the Ru^IV-Ru^VI transition (which catalyses the oxidation of streptomycin and neomycin), novobiocin could be detected at a lower (+0.2 V) potential, with a sensitivity of 1.31 nA µM^–1. Detection limits of 1.5, 6.0 and 10 µM were obtained for streptomycin, novobiocin and neomycin, respectively. These catalytic surfaces can be renewed (by polishing), with a surface-to-surface reproducibility of 6.5% for the detection of 5 × 10^–5M streptomycin. The analytical application of RuO₂-modified carbon paste electrodes to the analysis of these antibiotics by flow injection was investigated, with a view to liquid chromatographic separation with electrochemical detection applications.