| The work described in this dissertation involves the fabrication and characterization of new electrochemical sensors for trace analysis. Initially, ring-disk ultramicro electrodes (RD-UME) were fabricated to serve as a sensor platform. In addition, a method was developed to improve the sensitivity of carbon electrodes for selenium(IV) by modifying them with copper-mercury (Cu/Hg) films.; Fabrication of the RD-UMEs involved several material chemistry techniques: chemical vapor deposition, metallo-organic deposition, and electropolymerization. First, carbon fibers were coated with silica by resistively heating carbon fibers while passing a gas phase mixture containing silica precursors over the hot fibers. Second, one-half of each silica-coated carbon fiber was dip-coated in a solution containing noble metallo-organic compounds, and baked in an annealing oven, forming a thin, metallized carbon film. Finally, this film was sealed by electropolymerizing 2-allylphenol, forming nonconductive polymer at the electrode surface.; Scanning electron and optical microscopy were used to characterize silica, metallized carbon, and polymer films. After attaching independent electrical leads to the metallized carbon film and the carbon fiber, cyclic voltammetry was used to evaluate the quality of the individual electrodes, as well as their combinations in three- and two-electrode cells.; After fabricating dual electrodes, electrochemical sensors were developed for detecting selenium(IV). Specifically, electrodes were modified with electrodeposited Cu/Hg films. The modified electrodes possess interesting hybrid characteristics that are useful for sensor applications. As an amalgam of copper and mercury, Cu/Hg films exhibit properties of both metals. Comparable to copper, the films will oxidize to form aqueous copper ions. At the same time, the electrodes modified with Cu/Hg films have a hydrogen over-potential comparable to mercury film electrodes.; Following characterization, the modified electrodes were used as selenium(IV) sensors and were found to have improved sensitivity compared to mercury film electrodes. While other electrode substrates were tested, a carbon fiber UME modified with a Cu/Hg film was the most effective selenium(IV) sensor with a limit of detection of 23.2 ppb. |
