Optoelectrochemical sensor for lead based on electrochemically assisted solvent extraction

A thin film containing the complexing agent 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol (BrPADAP) deposited on the surface of an indium tin oxide (ITO) electrode has been used as a colorimetric sensor for lead. The sensor is based on a new electrochemically assisted solvent extraction method. When a cathodic potential was applied to the thin-film sensing layer, lead ions were extracted from the aqueous solution into the film resulting in an increase of absorbance at 550 nm. The magnitude of the absorbance change was linearly dependent on the concentration of lead in the range 0–5 ppm with an estimated limit of detection for a simple spectrophotometric method better than 250 ppb. The sensor was reset for a fresh measurement by applying an anodic potential. The prospects for using this electroassisted extraction method in conjunction with the optical waveguide evanescent field detection as a new integrated sensor for trace analysis are discussed. A sensitivity better than 10 ppb is predicted for this configuration.