Differential pulse anodic stripping voltammetric determination of traces of copper with a tobramycin-Nafion modified electrode.
A Nafion-modified glassy carbon electrode incorporated with tobramycin for the voltammetric stripping determination of Cu2+ has been explored. The electrode was fabricated by tobramycin containing Nafion on the glassy carbon electrode surface. The modified electrode exhibited a significantly increased sensitivity and selectivity for Cu2+ compared with a bare glassy carbon electrode and the Nafion modified electrode. Cu2+ was accumulated in HAc-NaAc buffer (pH 4.6) at a potential of -0.6 V (vs. SCE) for 300 s and then determined by differential pulse anodic stripping voltammetry. The effects of various parameters, such as the mass of Nafion, the concentration of tobramycin, the pH of the medium, the accumulation potential, the accumulation time and the scan rate, were investigated. Under the optimum conditions, a linear calibration graph was obtained in the concentration range of 1.0 x 10(-9) to 5.0 x 10(-7) mol l(-1) with a correlation coefficient of 0.9971. The relative standard deviations for eight successive determinations were 4.3 and 2.9% for 1.0 x 10(-8) and 2.0 x 10(-7) mol l(-1) Cu2+, respectively. The detection limit (three times signal to noise) was 5.0 x 10(-10) mol l(-1). A study of interfering substances was also performed, and the method was applied to the direct determination of copper in water samples, and also in analytical reagent-grade salts with satisfactory results.
MULTIELECTROCHROMIC PROPERTIES OF METHYLENE BLUE AND PHENOSAFRANINE DYES INCORPORATED INTO NAFION FILM
Abstract The electrochemical and spectroelectrochemical properties of phenosafranine (a phenazine dye) (PS + ) and methylene blue (a phenothiazine dye) (MB + ) immobilized into Nafion® (Nf) film were studied in 0.5 M H 2 SO 4 . The PS + dye was readily incorporated into Nf film containing MB + or vice versa, presumably by electrostatic interaction with the free sulfonate (SO 3 − ) groups and hydrophobic interaction with the fluorocarbon moieties of the Nf film. The interaction of these dyes with the hydrophobic fluorocarbon moieties could be understood from their observed higher concentration than the available sulfonate groups in the Nf film and also from their stable redox behavior. On the other hand, thionine (TH + ), another member of the phenothiazine family, was partially leached from the Nf film when the incorporation of PS + was followed because of its weak interaction with the hydrophobic fluorocarbon moieties of the Nf film. The PS incorporated Nf film containing MB + (Nf/PS + /MB + ) showed two well-separated reversible redox waves at 0.22 and −0.05 V (SCE) due to the redox process of MB + and PS + , respectively. The amount of dye molecules in the Nf film could be varied by changing the concentration of dye molecules in the immersion solution. The Nf/PS + /MB + film showed highly stable reversible color changes upon repeated cycles of applied potentials when compared to the Nf film with incorporated TH + and PS + dyes (Nf/TH + / PS + ). The changes in the absorbance of Nf/PS + /MB + film were accompanied with visible reversible changes of film color, ranging from blue-red at 0.7 V to red at 0.0 V and colorless at −0.5 V(SCE) due to the reversible redox process of the MB + and PS + dyes in the Nf film.
Dehydration of protonated Nafion® coatings induced by cation exchange and monitored by quartz crystal microgravimetry
Abstract A quartz crystal microbalance was employed to monitor the changes in mass of thin protonated Nafion® coatings during the replacement of the protons by other cations. In almost every case the mass of the coatings decreased during the cation exchange, despite the replacement of the protons in the coatings with much more massive cations. The expulsion of water from the coatings, induced by the cation exchange, was responsible for the decreases in mass. With simple aqua cations the quantities of water expelled per cation exchanged were relatively small. However, for multiply charged hexaammine and 2,2′-bipyridine complexes as many as 50 water molecules were shown to be ejected from the coatings for each incorporated cation. Data for the cation exchange of 18 cations are presented and some possible reasons for the accompanying dehydration of the coatings are suggested.