Hydrodynamic potential-modulated reflectance spectroscopy: Theory and experiment

This article describes the development and application of a new electrochem ical methodology based on potential-modulated UV-vis reflectance spectrosco py (PMRS). The device configuration is based upon a thin-layer flow-through channel cell incorporating a platinum working electrode. Reagent solutions are pumped through the cell under well-defined hydrodynamic conditions and electrolyzed at the platinum working electrode. Measurements are presented for linear sweep and fixed de potentials with a superimposed small amplitu de sinusoidal potential perturbation. A UV-vis source is employed to irradi ate the electrode region, and the resulting reflected signal is analyzed us ing a phase sensitive detector. Experimental studies using tris(4-bromophen yl) amine (TBPA) in acetonitrile are presented which quantify the relations hip between the absorption spectrum and reflected light intensity as a func tion of the transport rate, electrolysis reactions, and the modulation freq uency of the incident irradiation. The experimental results are analyzed us ing numerical simulations based on a finite difference strategy. These perm it the quantitative prediction of the concentration distribution of reagent s within the cell. A fast Fourier transform (FFT) routine was used to analy ze the frequency response of the numerically predicted reflectance signal. Excellent agreement was observed between the numerical predictions and expe rimental observations.