Slow scan voltammetry for diffusion-controlled currents in sodium alginate solutions

• Slow scan voltammetry discerns diffusion-controlled current from capacitive one.
• Sodium alginate suppresses natural convection, retaining diffusion current.
• Voltammetry at 0.1 mV/s in sodium alginate allows us to determine 0.5 μM.

Slow scan voltammetry is useful for extracting Faradaic diffusion-controlled current from capacitive one, because the former and the latter are, respectively, proportional to the square-root of scan rate and the scan rate itself. This report shows clear, reproducible voltammograms of 0.5 μM redox species with the help of sodium alginate (SA) at scan rates less than 0.1 mV s−1. SA enhances viscosity of solution without any influence on diffusion coefficient of the redox species so that natural convention is suppressed during the slow scan. Therefore, it allowed us to obtain ideal voltammograms reproducibly at slow scans, retaining the Faradaic current. Especially, a wire electrode is demonstrated to be a powerful tool for detecting low concentrations by slow scan voltammetry because of the large electrode area in comparison with the length of the boundary between the electrode and the insulator. A voltammetric detection limit is obtained in the relationship between the scan rates and concentration of redox species.

Reduction waves of Fe(CN)64- in solution with and without sodium alginate at 0.3 mV/s.Figure optionsDownload as PowerPoint slide