Liquid Membrane Ion-selective Electrodes Research Articles

Construction of ion-selective electrodes for chlorpromazine, amitriptyline, propantheline and meperidine: analytical study and application to pharmaceutical analysis.

Liquid-membrane ion-selective electrodes that respond to the cationic forms of chlorpromazine, amitriptyline and meperidine and to the quaternary ammonium compound propantheline are described. The liquid ion exchangers used were the salts of chlorpromazine or amitriptyline with eosin and tetraphenylborate in p-nitrocumene, propantheline with tetraphenylborate in 2-nitrotoluene and meperidine with tetrakis(m-chlorophenyl)borate in p-nitrocumene. The electrodes exhibited near-Nernstian response in the range 6 × 10–3–4 × 10–5M, working pH range 1–6 (chlorpromazine); 6 × 10–3–6 × 10–5M, pH 1–6 (amitriptyline); 6 × 10–3–3 × 10–6M, pH 1–9 (propantheline); and 10–2–7 × 10–6M, pH 1–7 (meperidine). The interferences from the alkali and alkaline earth metals were negligible but cationic molecules of similar structure interfered strongly. The electrodes were applied successfully to the assay of active compounds in pharmaceutical preparations. The major advantages of the proposed methods are their simplicity and speed.

Exchange current determination and time-dependent effects for model liquid membrane ion-selective electrodes

Exchange currents have been determined using impedance measurements on liquid membranes consisting of a solution of valinomycin in 2,3-dimethylnitrobenzene, supported on a cellulose acetate filter. Various time-dependent effects have also been investigated by the same method. This valinomycin-based membrane provides a model system for some commercial ion-selective electrodes. The results indicate that potassium ions readily cross the water/liquid membrane interface, whilst sodium ions are largely excluded from the membrane. A complex situation appears to exist, whereby a general increase in bulk membrane resistance is offset to a greater or lesser extent (depending on the cation in the contacting solutions) by a reduction in resistance of the membrane phase due to cation uptake.

The Theory of Liquid Ion-exchange Membrane Ion-selective Electrodes Based on the Concept of the Mixed Ion-transfer Potential

Abstract The theory of liquid ion-exchange membrane ion-selective electrodes has been developed on the basis of the concept of the zero-current potential, or the mixed potential in the presence of interfering ions, of ion transfer at the interface between a liquid membrane and a sample solution. Under the assumptions of the reversible ion transfer at the interface, the presence of supporting electrolytes in both phases, and the monovalency of all relevant ions, theoretical equations for the mixed potential are derived for two cases; the primary and interfering ions have 1) the same charge sign and 2) the opposite sign. The selectivity coefficients of the ion-selective electrodes can be expressed as a function of the difference between the standard ion-transfer potentials of the primary and interfering ions, the ratios of the mass-transfer coefficients of the ions, and the ratios of the concentrations of the ions. The theoretical prediction has been shown to be applicable to an interpretation of the response of liquid-membrane ion-selective electrodes.

Cholate liquid membrane ion-selective electrode for drug analysis

A cholate liquid membrane electrode employing benzyldimethylcetylammonium cholate as sensor was prepared, characterised and applied to the analysis of commercially available drugs containing cholanic acids. The results are comparable to those obtained using a benzoate electrode.

Determination of novocaine in pharmaceutical preparations with novocaine +-selective membrane electrodes

Liquid-membrane ion-selective electrodes made with the ion-association complexes of novocaine with tetraphenylborate or dipicrylamine are proposed for use in the determination of novocaine by direct potentiometry or by potentiometric titration with sodium tetraphenylborate. The titration method is preferred, and the mean relative error for 4–12 mg of novocaine hydrochloride is 0.5%.

Ion transport in free and supported nitrobenzene aliquat nitrate liquid membrane ion-selective electrodes : I. Bulk electrical properties including ion association and dielectric constant

A controlled-thickness thin layer cell and wide-band cross correlator bridge have been used to characterize ion transport in free liquid and supported ion exchange membranes. The base system of Aliquat nitrate in nitrobenzene was measured, and transport parameters were used to establish properties of supports: cellulose triacetate, PVC-acrylonitrile, polypropylene and Teflon. From DC to 0.5 MHz impedance measurements, geometrical capacitance, electrical relaxation time constants and dielectric constants were determined over a range of temperatures and membrane loadings. Depression of dielectric constant with loading and temperature coefficients are reported. Conductivities were analyzed classically to yield equivalent conductances of ions, transference numbers and ion pairing constants. Temperature coefficients gave transport enthalpy and thermodynamic quantities. Data from supported membranes gave direct measures of void volumes of inert membrane supports, and clear evidence for cases of membrane solubilization by entrapped solvents.

An improved ion-selective electrode for perchlorate

A new liquid-membrane ion-selective electrode for perchlorate ion based on tetrakistri-phenylphosphine silver(I) perchlorate in nitrobenzene is described. Its dynamic range and selectivities relative to most common anions are comparable to those of the Orion model 92–81 perchlorate sensor. However, it suffers much less hydroxide-ion interference than the Orion product.

Selectivity coefficient changes for liquid-membrane electrodes

The effects of the activity levels of the measured ion and interfering ions, and of the detection limit of the electrode on the values of selectivity coefficients for liquid-membrane ion-selective electrodes are discussed. The coefficients were determined by the mixed-ion solution method. Depending on the activity of the interfering ion, the activity of the main ion for which the selectivity coefficient is determined may differ. The best conditions of measurement are those which involve the largest contribution from the term containing the selectivity coefficient in the Nikolsky equation; the measurements are then most precise, and the values of the selectivity coefficients describe the electrode behaviour most consistently. When the limit of detection of the electrode is comparable with the other terms, it must be taken into account in calculations. Under the optimal conditions, selectivity coefficients were calculated for the Orion calcium and divalent cation electrodes, with calcium as the main ion and alkali metal ions as interfering ions.

Preparation and properties of a carbonate ion-selective membrane electrode

A liquid membrane ion-selective electrode has been prepared for the measurement of carbonate ion activities in solutions containing high levels of hydrogen carbonate and chloride. The electrode exhibits Nernstian response in the approximate range 1O -2–1O -7 M carbonate, and has a fast response and low noise level under most conditions. In the physiologically important pH region, hydroxide ion does not interfere. Detailed information is given on the composition and properties of the active membrane phase.