Optoelectrochemical sensor for lead based on electrochemically assisted solvent extraction

A thin film containing the complexing agent 2-(5-bromo-2-pyridylazo)-5-(die thylamino)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. Wh en a cathodic potential was applied to the thin-film sensing layer, lead io ns were extracted from the aqueous solution into the film resulting in an i ncrease 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 bett er than 250 ppb. The sensor was reset for a fresh measurement by applying a n anodic potential. The prospects for using this electroassisted extraction method in conjunction with the optical waveguide evanescent field detectio n as a new integrated sensor for trace analysis are discussed. A sensitivit y better than 10 ppb is predicted for this configuration. (C) 2000 Elsevier Science S.A. All rights reserved.