The exchange kinetics of Cs + , Cu 2+ , and Eu 3+ ions in Nafion-117 were measured at different H + ion concentrations in equilibrating salt solutions. The exchange kinetics were found to be independent of the H + ion concentration in equilibrating salt solutions over the pH range of 5-2. The exchange kinetics were therefore used to evaluate self-diffusion coefficients of the metal ions using an analytical solution of Fick's second law. The self-diffusion coefficient of Cs + in Nafion-117 was found to be in agreement with the value obtained in our earlier work (1.94 × 10 -7 cm 2 s -1 ) based on the isotopic-exchange method in the absence of H + ions. This further confirmed that the exchange process in the Nafion-117 membrane represents the pure isotopic exchange in the said pH range. The self-diffusion coefficients of Cu 2+ and Eu 3+ were found to be 2.9 × 10 -7 and 4.5 × 10 -8 cm 2 s -1 , respectively. The smaller self-diffusion coefficient of Eu 3+ reflects its increased electrostatic interaction with the membrane matrix. The kinetics of forward (H (m)n+ ) and reverse (M (m) n+ h H (s) + ) exchanges of metal ions (Cs + , Cu 2+ , and Eu 3+ ) in the Nafion-117 membrane were also studied. The Nernst-Planck theory was examined to predict the kinetics of these exchanges. The theory was found to be reasonably accurate for predicting the kinetics of the reverse ion exchange but completely failed for the forward ion exchange. Contrary to the prediction of the theory, the kinetics of forward exchanges of Cs + , Cu 2+ , and Eu 3+ with H + ions in the Nafion-117 membrane were found to be independent of the metal ions. This shows that the self-diffusion coefficients of the counterions in Nafion-117 can be obtained only from the analysis of reverse exchange kinetics based on the Nernst-Planck equation.

Glass-supported films of lipids and polydiacetylene were applied for visual detection and colorimetric fingerprinting of bacteria. The sensor films comprise polydiacetylene domains serving as the chromatic reporter interspersed within lipid monolayers that function as a biomimetic membrane platform. The detection schemes are based on either visible blue-red transitions or fluorescence transformations of polydiacetylene, induced by amphiphilic molecules secreted by proliferating bacteria. An important feature of the new film platform is the feasibility of either naked-eye detection of bacteria or color analysis using conventional scanners. Furthermore, we find that the degrees of bacterially induced color transformations depend both on the bacterial strains examined and the lipid compositions of the films. Accordingly, bacterial fingerprinting can be achieved through pattern recognition obtained by recording the chromatic transformations in an array of lipid/PDA films having different lipid components.

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A method for sorption preconcentration of Cr(VI) from aqueous samples was developed using a polymer inclusion sorbent (PIS). The PIS used in this method was prepared by physical inclusion of Aliquat-336 in the matrix formed by cellulose triacetate and 2-nitrophenyl octyl ether. This sorbent was found to be stable, cost-effective, efficient for preconcentration of Cr(VI) present in the aqueous samples, and amenable to direct quantitative analysis of Cr(VI) held in it by neutron activation analysis and spectrophotometry. The quantifying of Cr(VI) in PIS by spectrophotometry was carried out by developing color directly on the PIS after reacting it with 1,5-diphenylcarbazide. The distinct color developed on the PIS even at very low concentrations of Cr(VI) suggests its possible use for field determination of Cr(VI). The composition of PIS was optimized to obtain maximum uptake of Cr(VI) without sacrificing uniformity in terms of thickness and distribution of ion-exchange sites, stability, and time required for quantitative sorption of Cr(VI) from aqueous samples. The Cr(VI) species held in the PIS, mainly HCrO4- and CrO4(2-), were found to vary as a function of pH of the aqueous samples from which Cr(VI) was preconcentrated. A close agreement was found in the abundances of Cr(VI) species held in the PIS with those reported in the literature for aqueous solutions at different pH. The variation of Cr(VI) species as a function of pH was found to have a significant impact on the tolerance to anions on the uptake of Cr(VI) in the PIS. The high selectivity of PIS toward Cr(VI) from aqueous solution at pH = 2 was explained on the basis of hydration of anions. The uptake of Cr(VI) was found to be fairly constant (88 +/- 3%) up to nearly complete exchange of counterions present in the PIS. The method developed in the present work was successfully used for the preconcentration of Cr(VI) from tap water and seawater samples containing low levels of Cr(VI).

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