Development of electrochemical and spectroelectrochemical sensors for lead(II) and rhenium(bis(dimethylphosphino)ethane)

In this dissertation, experiments, results, and pertinent information on several research topics are provided. First, a mercury-free Nafion-modified graphite electrode incorporated with 1-(2-pyridylazo)-2-naphthol (PAN) for anodic stripping determination of Pb(II) has been explored. The potential utility of the PAN-incorporated Nafion-modified electrode for the determination of Pb(II) is demonstrated. The effect of surfactants sodium dodecyl sulfate and Triton X-100 on the voltammetric response of the electrodes was also investigated. Second, Nafion or sodium poly(styrene sulfonate) entrapped in either sol-gel-derived silica or cross-linked poly(vinyl alcohol) composite coatings on spectroscopic graphite electrodes were investigated electrochemically with [ReI(DMPE) 3]+, where DMPE = 1,2-bis(dimethylphosphino)ethane. It is shown that dispersing Nafion in sol-gel-derived silica matrix significantly improves the slow diffusion of [ReI(DMPE)3] + in Nafion, thus furnishing a higher sensitivity than Nafion in a shorter preconcentration time. Third, the influence of the composition of Nafion-silica composite on electrochemical response of the composite-modified electrodes to [ReI(DMPE)3]+ were investigated. Both Nafion content and initial composition of the sol affect the accessibility of the active sites of Nafion in the composite to [Re I(DMPE)3]+, and thus the increase rate of electrochemical signal during preconcentration of [ReI(DMPE) 3]+. The suitability of the developed Nafion-silica composite for three-mode-selectivity spectroelectrochemical sensing of [ReI(DMPE) 3]+ is demonstrated. Fourth, the utility of microelectrodes for oxidation state speciation of redox couples has been explored. The speciation of the model redox couple, [Fe(CN)6]3-/[Fe(CN) 6]4-, is demonstrated at bare carbon-fiber microelectrodes of ca. 5 mum in radius, whereas the applicability of chemically modified microelectrodes for oxidation state speciation is demonstrated with Nafion-silica composite modified microelectrodes for [ReI(DMPE)3] +/[ReII(DMPE)3]2+. Finally, the formation and electrochemical behavior of self-assembled monolayers (SAMs) formed from n-dodecanethiol and terminally functionalized short-chain thiols on gold have been investigated. It is shown that the influence of terminally functionalized short-chain thiols on heterogeneous electron transfer depends on the chain length and the terminal group of a thiol, solution conditions, and the intrinsic heterogeneous electron transfer rate of a redox couple. Two-component monolayers assembled either simultaneously or sequentially with a long-chain n-alkanethiol and a terminally functionalized short-chain thiol were also explored for potential sensing of electroactive species.