John N. Richardson

Spectroelectrochemical Sensing Based on Attenuated Total Internal Reflectance Stripping Voltammetry. 3. Determination of Cadmium and Copper

The optical and electrochemical properties of metallic films on ITO surfaces resulting from deposition of copper and cadmium were monitored by stripping voltammetry-attenuated internal reflectance spectroscopy. The voltammetric or optical responses of both metals were examined with respect to solution conditions such as pH and presence of dissolved oxygen. The morphologies of these films were also examined using environmental scanning electron microscopy, and the microscopic electrodeposition patterns were found to influence the optical response. The wavelength dependence of the optical response of deposited copper was determined and compared with calculations; optimal performance was at 400 nm for copper. A linear calibration curve was obtained over a range of 1 x 10(-7)-1 x 10(-4) M for copper and compared with that of cadmium. The simultaneous determination of cadmium and copper was demonstrated, and the mechanism of co-deposition is discussed.

A simple optical sensor for chromium(VI) based on a cationic ion exchange film coupled with attenuated total reflectance spectroscopy

A new optical sensor for Cr(VI) in environmental water samples has been developed. The device is based on uptake of Cr(VI) as at acidic pH into a quaternized poly(4-vinylpyridine) (QPVP) film followed by direct optical detection using attenuated total reflectance (ATR) spectroscopy in a thin-layer flow cell. Cr(VI) uptake is demonstrated to be reversible such that the film can be regenerated for multiple uses over extended periods of time. The sensor was investigated over a pH range of 3–7 and gave a linear response over a Cr(VI) concentration range of 5 µM to 1 mM at pH 4. Analysis of potential interferences demonstrates that the sensor provides excellent discrimination against cationic species, including Cr(III). We also demonstrate a prototype ‘field ready’ version of the sensor utilizing a 410-nm light-emitting diode source, fixed angles, and prismless construction that is used in conjunction with a rugged miniature spectrometer.

Development and Application of Novel Thin-Film Spectroelectrochemical Sensors Possessing Three Modes of Selectivity*

A thin-film spectroelectrochemical sensor design employing three modes of selectivity is described. Selectivity is achieved through (1) partitioning of the analyte into a chemically selective film, (2) electrochemical cycling of the analyte over a given potential window, and (3) absorbance of one of the redox states of the analyte at the chosen analytical wavelength. Optimization of the sensor is described with respect to both improved selectivity and sensitivity, as well as its response to a number of different chemical species. Lastly, application of the sensor for determination of ferrocyanide, Fe(CN)4-6, in both radioactive waste simulant and actual waste storage tank contents is given.