Mixed Ion Solutions Research Articles

Selectivity of Polymer Membrane-Based Ion-Selective Electrodes: Self-Consistent Model Describing the Potentiometric Response in Mixed Ion Solutions of Different Charge

Despite its well-documented limitations, the semiempirical Nicolsky-Eisenman equation is used throughout the existing analytical literature to describe the selectivity of modern polymer membrane-based ion-selective electrodes (ISEs). In this paper, a new quantitative description for the response/selectivity function based on ion-extraction equilibria at the sample/membrane interface is presented. The proposed selectivity formalism clearly illustrates the range of validity for the conventional Nicolsky-Eisenman formalism. Extended equations are derived describing the electrode response in an exact manner, particularly with respect to analyte and interfering ions of different charge. The expression obtained corresponds to the matched potential method proposed previously by Christian and co-workers on the basis of solely empirical observations. Selectivity coefficients required for a given analytical problem with a predefined maximum error can now be predicted more accurately. Such predictions with respect to analyte and interfering ions of varying charges differ by 1-2 orders of magnitude in comparison to the selectivity values required on the basis of the extended Nicolsky-Eisenman formalism.

Ionic partition equilibrium in a charged membrane immersed in a mixed ionic solution

In partition equilibria of Ca2+, K+ and Cl– between a swollen charged membrane and an aqueous bath of mixed KCl and CaCl2 electrolytes, the equilibrium concentration of the bivalent ion in the membrane decreases to a minimum value as its concentration in the bath increases. The value of the concentration minimum decreases with increasing KCl : CaCl2 concentration ratio in the bath. Simulations and analysis have been performed on the basis of Donnan distribution theory.

Ion chromatographic determination of inorganic anions with a simple suppressor system.

A simple suppression method using an anion micromembrane suppressor (Dionex AMMS) has been developed for ion chromatography (IC) with the conductometric detector. An outline of the suppression method is described below. Two air-tight glass bottles were used as a scavenger tank and an eluent waste tank, respectively and were connected with a Teflon tube (0.5 mm i.d. × 120 mm). The scavenger flow was driven by the air-pressure induced by the introduction of the eluent into the waste tank, along with the siphon effect caused by placing the suppressor 30 cm higher than the AMMS. With these conditions the flow rate of the scavenger was 1.2 ml/min and remained constant for over 6 h. When 1 mM NaOH-0.4 mM Na2CO3-1% CH3OH solution was used as an eluent, a satisfactory determination of inorganic anions was achieved with the simple suppressor-IC system using a column of porous polymethacrylate gel (PCI-201S, TOA) with the following conditions : flow rate, 1.2 ml/min ; scavenger, 12.5 mM H2SO4 solution; column temperature, 30°C. A hydrogencarbonate ion peak appeared after that of the nitrate ion peak under the conditions given above. Calibration curves for the peak areas of 8 anions (F -, Cl-, NO2 -, Br-, NO3 -, HPO4 2-, SO4 2- and I -) showed good linearity and the relative standard deviation (RSD) of the standard mixed-ion solution was found to be 0.4 to 1.3% (n =9).

還元剤添加示差原子吸光分析法によるＣｒ（ＩＩＩ），（ＩＶ）の定量とクロムめっき浴分析への応用

A previous papers reported on the enhancing effects of metal hydrides for the determination of metals that require high atomization temperature such as beryllium salt by flameless atomic absorption spectrometry in N, N-dimethylformamide (DMF).The present paper proposes a method of quantitative estimation of mixing ratios in mixed solutions chromium (III) and (VI) ions by flameless atomic absorption spectrometry, utilizing the different effects lithium hydride and sodium boro hydride by in DMF.That is to say the relation between increased sensitivity and the amount of lithium hydride added differed for chromium (III) and chromium (VI) ion. A calibration curve was drawn for each ion concentration, and the ratio of chromium (III) and chromium (VI) ions in the solution was determined by using the difference in the effects of lithium hydride on the two ions. The proposed method provided a satisfactory analytical result for chromium (III) and (VI) in general chromium plating baths.The coefficient of variation by this method was 4.4% (n=5) for a mixed ion solution containing 0.5ppm chromium.

Dielectric properties of NaCl1−xBr and KCl1−xBrx mixed ionic solution

In the present paper a three-body potential model (TBPM) has been employed for the analysis of dielectric behaviour of NaCl-NaBr and and KCl-KBr mixed crystals with varying compositions. The physical properties like dielectric constants (ɛ0 andɛ∞), optic mode frequencies (ΩOLO andΩTO), effective charge parameter (es*), optic mode Gruneisen parameters and strain derivatives ofɛ0 andɛ∞ dielectric constants have been calculated. The results achieved in the present study are found in fairly good agreement with the available experimental data. The results obtained by previous investigators are also shown for the sake of comparison.

Sorption and retention of Pb, Cu and Cd ions in three species of mosses used for air pollution studies in Nigeria

The capacities of the mosses Rhacopilopsis trinitensis (C. Muell) Britt.et Dix., Stereophyllum virens Card., and Thuidium gratum (C. Muell) Jaeg. to sorb and retain Pb, Cu and Cd ions from solution were studied. All the species showed very high capacities to sorb these metal ions from single-ion as well as mixed-ion solutions. Ca and Mg ions were most readily released from the moss tissues on sorption of the metal ions. The sorbed metal ions were strongly retained in the moss tissues, but may be significantly leached out by strongly acidic solutions. The three species did not differ remarkably in their capacities to sorb and retain the metal ions.

Evidence for the existence of complex ions in mixed solutions of indium trichloride and ammonium chloride

The conductances, densities, and viscosities of concentrated solutions of ammonium chloride in water, at 25 °C, have been determined with good agreement with existing conductance data. The same data have been obtained for mixed solutions of indium trichloride and ammonium chloride. The fact that the conductance is always much less than the sum of the individual conductances, in some cases less than that of indium chloride alone, points to the existence of a complex in solution.

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.

Activity coefficients of calcium ions in mixed solutions.

Activity coefficients of calcium ions in mixed solutions.