Real time measurement of concentration ratio at an electrode/solution interface by calculating the inverse Laplace transform of SOWG spectroscopy

A novel technique for measuring the concentration rate of a redox compound at an electrode/solution interface was developed using slab optical waveguide (SOWG) spectroscopy. The electrolysis of 5 mmol dm−3 ferroin in 1 mol dm−3 potassium nitrate solution was carried out on an indium-tin oxide (ITO) electrode and plastic-formed carbon (PFC) electrode by cyclic voltammetry, using each spectroelectrochemical cell in SOWG spectroscopy. Their SOWG spectra were obtained every 0.05 mV during the potential sweep between +0.4 and +1.4 V for the ITO electrode and between +0.4 and +1.2 V for the PFC electrode. To obtain the concentration profiles near the electrode during the cyclic voltammetry of ferroin, the SOWG spectra were converted to concentration ratios at given locations, and these ratios were plotted against a penetration depth of evanescent wave. The theoretical derived concentration–distance profiles during CV were experimentally verified by the present technique.