Elzbieta Malinowska

ANION-SELECTIVE MEMBRANE ELECTRODES BASED ON METALLOPORPHYRINS: THE INFLUENCE OF LIPOPHILIC ANIONIC AND CATIONIC SITES ON POTENTIOMETRIC SELECTIVITY

The role of lipophilic anionic and cationic additives on the potentiometric anion selectivities of polymer membrane electrodes prepared with various metalloporphyrins as anion selective ionophores is examined. The presence of lipophilic anionic sites (e.g. tetraphenylborate derivatives) is shown to enhance the non-Hofmeister anion selectivities of membranes doped with In(III) and Sn(IV) porphyrins. In contrast, membranes containing Co(III) porphyrins require the addition of lipophilic cationic sites (e.g. tridodecylmethylammonium ions) in order to achieve optimal anion selectivity (for nitrite and thiocyanate) as well as rapid and reversible Nernstian response toward these anionic species. These experimental results coupled with appropriate theoretical models that predict the effect of lipophilic anion and cation sites on the selectivities of membranes doped with either neutral or charged carrier type ionophores may be used to determine the operative ionophore mechanism of each metalloporphyrin complex within the organic membrane phase.

Role of axial ligation on potentiometric response of Co(III) tetraphenylporphyrin-doped polymeric membranes to nitrite ions

Abstract Two types of Co(III) tetraphenylporphyrins, Co(III)TPPX (I) and Co(III)(N)TPPX (II), where X = C1− or NO−2 and N = C5H5N or C6H5CH2C5H4N, are used as ionophores to prepare nitrite responsive polymeric membrane electrodes. The influence of the initial axial ligand (X− and N) on the operative ionophore mechanism of these metalloporphyrins within the solvent polymeric membranes is examined. Results from potentiometric and electrodialysis experiments suggest that in the presence of nitrite in the test sample and internal solution, both types of Co (III) porphyrins studied (I and II) act as neutral carriers and that the addition of lipophilic cationic sites (e.g., tridodecylmethylammonium ions (TDMA+)) to the organic membrane is essential to improve the selectivity and long term stability of sensors prepared with these species. Membranes formulated with (I) or (II) in the nitrite form along with TDMACl in plasticized PVC films exhibit the following selectivity sequence: SCN− > NO−2 ~ C1O−4 > Sal− > NO−3 > Br− > C1−. Membrane electrodes with added lipophilic cationic sites are shown to exhibit rapid, fully reversible and Nernstian response towards nitrite ions in the concentration range of 10−1–10−5 M, with good long term stability.

Enhanced electrochemical performance of solid-state ion sensors based on silicone rubber membranes

Results of optimization studies regarding the composition of silicone rubber films suitable for preparing miniaturized solid-state ion-selective sensors are presented. Using conventional macro ion-selective electrodes (ISEs) it was shown that the addition of more lipophilic ionic additives and small amounts of an appropriate plasticizer to the silicone matrix achieved optimal electroanalytical performance. The incorporation of these components into the membrane along with the required ionophore can, however, influence membrane curing time and adhesion of the film to silicon nitride surfaces. Solid-state sensors with optimized silicone membrane compositions exhibit theoretical and reproducible electrochemical performance.

Calix[4]arene derived tetraester receptors modified at their wide rim by polymerizable groups

The synthesis of calix[4]arene tetraester ionophores containing polymerizable groups at their wider rim is reported. Calixarene monomers with one or two methacrylamide groups were copolymerized with methyl methacrylate, yielding linear polymers with pendant calixarene groups or crosslinked polymers. Extraction studies with the soluble copolymers and with the corresponding pivalamides as model compounds showed no difference in the extraction ability and selectivity. Potentiometric measurements of membrane electrodes prepared with the polymeric calixarene ionophores indicated that the high selectivity, the slope of the response curve and the low detection limit of membranes containing non-bonded calixarene ionophores are retained while the lifetime of the polymeric membranes is increased.

Improved stability of solid-state ion-selective sensors by incorporation of lipophilic silver-calix[4] arene complexers within polymeric films

The EMF stability of potentiometric solid-state ion-selective sensors is found to be enhanced by the incorporation of lipophilic silver-ligand complex of thioether derivatized calix[4]arene [Ag(TDC)+]. The membranes are made by adding silver-ligand complex with excess of free ligand (TDC) to polymer membrane doped with an appropriate ion-selective ionophore and ionic additives. The silver-ligand complex functions as a reversible electron transfer pair at the membrane-solid (Ag/sup 0/-epoxy) interface. The resulting solid-state sensors exhibit improved EMF stability during the first 20 hours of soaking in a solution of analyte ion and also continued to show improved stability over a 30-day period.

Enhanced Electrochemical Performance Of Solid-state Ion Sensors Based On Silicone Rubber Membranes

Results of optimization studies regarding the composition of silicone rubber films suitable for preparing miniaturized solid-state ion-selective sensors are presented. Using conventional macro ion-selective electrodes (ISE) it was shown that more lipophilic ionic additive species and the addition of small amounts of appropriate plasticizer to the silicone matrix is required to achieve optimal electroanalytical performance. The incorporation of these components into the membrane along with the required ionophore can, however, influence membrane curing time and adhesion of the film to silicone nitride surfaces. Solid-state sensors with optimized silicone membrane compositions exhibit theoretical and reproducible electrochemical performance.