Spectroscopic and electrochemical evaluation of a perfluorosulfonated ionomer and its gel as preconcentrating media for [ReI(DMPE)3]+, where DMPE = 1,2-bis(dimethylphosphino)ethane

The interaction of [Re-I(DMPE)(3)](+), where DMPE = 1,2-bis(dimethylphosphino)ethane, a nonradioactive analogue of a heart imaging agent, with Nafion gel, which is Nafion plasticized with tri-n-butyl phosphate, has been evaluated spectroscopically and electrochemically. Thin-layer spectroelectrochemistry on the rhenium compound yields a linear Nernst plot with an n value of 0.99 and E;' of 0.049 V vs Ag/AgCl. The electrochemistry is consistent with a reversible one-electron transfer between the mono- and dicationic forms of the complex. The UV-visible spectrum of electrogenerated [Re-II(DMPE)(3)](2+) is identical to that obtained by air oxidation of [Re-I(DMPE)(3)](+). Thin, free-standing films of Nafion gel and Nafion that were sufficiently clear to record visible spectra were cast. Spectroscopic measurement of the partitioning of [Re-I(DMPE)(3)](+) from aqueous solution into these films shows a more rapid uptake of the complex by the Nafion gel. Preconcentraion factors into Nafion gel and Nafion were 350 and 50, respectively, after 4 h of soaking. Cyclic voltammetry of 1.0 x 10(-4)-1.0 x 10(-7) M [Re-I(DMPE)(3)](+) in 0.15 RI supporting electrolyte aqueous solution at bare gold and spectroscopic graphite electrodes suggests that the complex adsorbs to these electrodes. By comparison, the well-defined cyclic voltammograms at Nafion gelmodified electrodes exhibit diffusion-controlled behavior. The formal reduction potential at Nafion gel-modified electrodes is shifted positively compared to bare electrodes. A current enhancement of similar to 4 was observed at Nafion gel-modified spectroscopic graphite over a bare electrode. A calibration plot of peak current for differential pulse voltammetry vs concentration at Nafion gelmodified spectroscopic graphite was linear in the 10(-7)-10(-5) M concentration range, with a detectable signal down into the 10(-9) M range.