The lifetime of the polymer membrane ion-selective electrode is, in general, short when compared to that of the glass pH electrode. It is the manner in which the elctroactive materials are entrapped in the ion-selective membranes which accounts for this lifetime difference. In the polymer membrane electrode a high molecular weight electroactive material is dissolved in the plasticized polymer membrane. Because it is hydrophobic, this material is much more compatible with the low dielectric membrane phase than with the aqueous analyte phase. It, of course, has some solubility in the aqueous phase and, in time, leaches from the membrane. In the glass pH electrode, the electroactive material is the SiOH group which is covalently attached to the insoluble glass membrane. Because it is attached, it cannot be leached from the membrane. The purpose of this study was to investigate the possibility of covalently attaching the electroactive material to the polymer membrane in polymer membrane electrodes. In this weay, it was hoped that electrodes with much longer lifetimes could be obtained. Cation selective electrodes based on sulfonated polystyrene were investigated first. Sulfonation was accomplished by dipping polystyrene membranes into chlorosulfonic acid. Electrodes of both the conventional (i.e., with internal reference) and coated-wire types were prepared. Neither gave satisfactory response. Cation selective electrodes based on the perfluorinated, sulfonic acid containing ion exchange polymer NAFION 120® were investigated next. This material produced well-behaved Cs⁺ electrodes but electrodes responsive to larger cations (e.g., tetrapropylammonium and dodecyltri-methylammonium) could not be obtained. This may be due to ion-pairing in the membrane phase between these larger cations and the polymer bound sulfonate groups. To help answer some of the questions encountered during these investigations of electrodes based on covalently attached sulfonate groups, polymer membrane electrodes based on dinonylnaphthalenesulfonic acid were prepared and investigated. These electrodes were found to have very great selectivity for high molecular weight organic cations relative to inorganic and smaller organic cations. This type of selectivity is analogous to that obtained in ion pair solvent extraction of cations with a high molecular weight anionic species. Since a number of species of clinical, biological and toxicological interest are, at physiological pH, high molecular weight organic cations, electrodes based on dinonylnaphthalenesulfonic acid show great promise for determination of such species. An electrode for the determination of the drug phencyclidine was prepared to demonstrate the potentialities of drug analysis with this type of electrode. A microcomputer-based potentiometric analysis system was used to collect and analyze the data in this study. This system was one of the first stand-alone microcomputer systems employing a high level computer language to be described. The IMSAI 8080 Microcomputer and the computer language CONVERS were used.

No description available.

Thesis (M.S.) -- Mississippi State University. Dave C. Swalm School of Chemical Engineering. / Title from title screen. Includes bibliographical references.

Thesis (M.Phil.) - University of Queensland, 2005. / Includes bibliography.

The nanoparticles of zirconium oxide, sulfated and phosphated zirconia were used to modify a Nafion membrane in order to improve its water retention, thermal stability, proton conductivity and methanol permeability so that it can be used at higher temperatures in fuel cell. These modified Nafion nanocomposite membrane with inorganic nanoparticles have been designed to run at operating temperatures between 120 oC and 140 oC because higher temperature operation reduces the impact of carbon monoxide poisoning, allows attainment of high power density and reduces cathode flooding as water is produced as vapor. The inorganic nanoparticles were incorporated within the Nafion matrix by recast, ion exchange and impregnation methods. The membrane properties were determined by ion exchange capacity (IEC), water uptake, methanol permeability and proton conductivity. The characterization of the inorganic nanoparticles within the nanocomposite membranes was determined by X-Ray diffraction (XRD), Brunau-Emmett-Teller (BET) surface area and Fourier transform infrared spectroscopy (FTIR) for structural properties. Thermal gravimetric analysis (TGA) and Differential scanning calorimetry (DSC) were used to determine the thermal properties, and the morphological properties were probed by Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM). Pristine ZrO2, sulfated and phosphated ZrO2 nanoparticles were synthesized successfully. The particle sizes ranged from 30 nm to 10 nm respectively. The resulted particles were incorporated to a Nafion membrane with good dispersity. The conductivity of the nanocomposite membrane were around 0.1037 S/cm at 25 oC with a higher water uptake of 42 %. These results were confirmed by the highest IEC value of 1.42 meg.g-1 of Nafion/ S-ZrO2 nanocomposites membrane. These high IEC value may due to the incorporation of superacid S-ZrO2 nanoparticles which increased the membrane acid property for providing new strong acid site. / Chemical Engineering / M. Tech. (Chemical Engineering)

Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Flow injection analysis (FIA) is a continuous flow technique developed in the early 1970's. FIA is based on reproducible sample injection, accurate timing and controlled dispersion. This technique is very versatile due to the control of the variables and can easily be automated. This technique is very suitable for routine laboratory analysis. By introducing various sample modifying techniques in tandem with the FIA system, samples can easily be modified. Some modifying techniques are analyte pre-concentration, sample dilution and sample cleanup. Passive dialysis can be used very successfully for sample dilution and cleanup. Problems arise when samples with low analyte concentration have to be analysed. For this reason an electrodialyser unit, equipped with a passive membrane, was developed. The history, development and theory of membranes and membrane processes are discussed. A study of the movement of ions, in solution and across a passive membrane, under the influence of an applied d.c. electrical potential is given. Passive membranes were evaluated for use in the proposed system. The following factors influencing the efficiency of electrodialysis in the F1 system were studies. The flow rate of the donor and acceptor channels; the applied d.c. electrical potential; injection loop volumes; flow direction in the electrodialyser unit. An investigation was done into on-line analyte pre-concentration and regulated dilution probabilities of the electrodialysis system. Systems that were evaluated are the following: The determination of chloride in water effluents; the determination of copper and zinc in pharmaceuticals; the direct and indirect determination of phosphate in fertilizers. A comparative study between the advantages and disadvantages of the passive dialysis and electrodialysis system is given. / Thesis (PhD (Chemistry))--University of Pretoria, 2006. / Chemistry / unrestricted

In this study we have investigated the frequency dependence of bilayer lipid membranes for a series of glycerylmonoolein/ n-decane bilayers in various aqueous ionic solutions containing the ionophore valinomycin. Reliable values of membrane capacitance and conductance were obtained over the frequency range 0.2 - 200 KHz using an automatic balancing bridge under the control of a microprocessor unit. The admittance data was then normalized and curve-fitted to produce relaxation times and amplitudes from which the kinetic rate parameters, as deduced from a single slab dielectric membrane model, were calculated. These ac experimental rate constants were then compared with those obtained from charge-pulse relaxation methods.

No description available.

A cation-responsive electrode system has been developed which incorporates aza-substituted crown ethers as ligands. In a novel application, uncomplexed crown ethers were used in the pelletized form for ionic transport. Electrodes have been produced which can be conditioned for a particular ion and following their use, be reconditioned and reused for other ions. Preparation method and lifetime studies are included. The responses of two crown ethers with plasticizers were evaluated for thirteen representative cations. The concentration range covered in each evaluation was 1 x 10-1 to 1 x 10-7 M. For those ions exhibiting Nernstian or near-Nernstian response, selectivity coefficients were derived.