Electropolymerization of 3,3'-diaminobenzidine at solid substrate electrodes (platinum, gold, and glassy carbon) gave stable and water-insoluble films under a wide range of pH. Under the conditions of this study, the polymer films were found to be electroactive in acidic solutions but not in neutral or basic solutions. The poly(3,3'diaminobenzidine)-modified gold electrode exhibited very high selectivity for the open circuit accumulation of Se-(IV) through complexation with the aromatic o-diamine groups attached to the polymer backbone to form the piaselenole. This property was exploited for the preconcentration of Se(IV), followed by differential pulse anodic stripping voltammetry for its determination. The differential pulse stripping analysis involved three steps: accumulation, electrochemical reduction to elemental selenium, and differential pulse anodic stripping. Factors affecting these steps were systematically investigated, and an optimized procedure was developed. Using this optimized procedure, a detection limit of 9.9 x 10-9 M Se-(IV) (0.78 ppb Se(IV)) was realized for a 10 min accumulation. For 10 determinations of Se(IV) at concentrations of 1.00 x 10-6 and 1.00 x 10-7 M, relative standard deviations of 2.8% and 3.4% were obtained, respectively. The presence of selected ions and complexing agents gave no observable interferences. Finally, the developed method was successfully applied to the analysis of selenium in a U.S. Environmental Protection Agency water quality control sample and also in a commercial health supplement sample.In the context of metal ions analyses, chemically modified electrodes possessing specifically functionalized surfaces have emerged as one of the most attractive areas for research.1-3 Among their advantages are their inherent high selectivity and sensitivity. Methods1-5 which have been used for electrode modification include physical coating, covalent attachment, incorporation of modifier into carbon paste, and electropolymerization. Of intrest here is electropolymerization, which offers an effective and versatile route for polymer film deposition on substrate electrodes. By judicious control of experimental variables, e.g., potential, time, concentration of monomer, nature of supporting (

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