The selectivity of an ion-selective electrode is determined by the:
AbstractA new method for the determination of the selectivity coefficient of an ion selective electrode is proposed. In the proposed method, a series of mixed solutions of the primary ion i and interfering ion j is prepared in which the sum of the logarithm of i concentration and logarithm of j concentration is kept constant. The potential of the electrode, E, is measured for the series of the mixed solutions. The result is plotted with the activity of i, ai, as abscissa against E on semi-logarithmic graph paper. The activity at the intersection of two extrapolated linear parts of the log a1-E curve is determined. From the activity at the intersection of the primary ion, the selectivity coefficient is calculated. The proposed method was applied to the determination of selectivity coefficients of fluoride, chloride, bromide and potassium selective electrodes. The selectivity coefficients determined by the proposed method, named “continuous variation method”, agreed with those obtained with the conventional mixed solution method. Show
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Rights and permissionsAbout this articleCite this articleHiiro, K., Wakida, Si. & Yamane, M. Determination of Selectivity Coefficients of Ion Selective Electrodes by Continuous Variation Method. ANAL. SCI. 4, 149–151 (1988). https://doi.org/10.2116/analsci.4.149 Download citation
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In general, it is a common feature of all analysis methods that when atoms or ions of a different species but with similar properties are also present, i.e. coexist with the atoms or ions of interest, they interfere with measurement. Do you recall the periodical table? Each column contains elements with similar properties. For example, Li, Na, and K etc. are the alkaline metals, which tend to form monovalent cations; Mg and Ca etc. are the alkaline-earth metals, which tend to form divalent cations; and F,
Cl, Br, and I etc. are the halogens, which tend to form monovalent anions. In addition, the elements Cu, Ag, Cd, and Pb, which tend to form monovalent and divalent cations, are aligned relatively close to each other both vertically and horizontally within the table. In addition, the effects of coexisting ions can be predicted to some extent from the response membrane material, that is to say, the reactivity of the response membrane material to the coexisting ions. For example, a solid-state membrane electrode can be seriously affected by coexisting ions that form insoluble compounds or complex salts with the material of its response membrane; and a liquid membrane electrode can be affected by coexisting ions that form ionic associates with the components in its response membrane. Example: Impact of coexisting ions on potassium ionsA potassium ion electrode can be affected by various types of ion species. The degree of this effect can be expressed by using selectivity coefficient K in the following formula: where aK+ is the potassium ion concentration, and ax is the interfering ion concentration. The smaller the value of K, the less the interference. The selectivity coefficients of typical interfering ions are listed in the table below. Please note that the selectivity coefficient varies depending on potassium ion concentration. The values in the table are for 10-3mol/L K+. The larger the potassium ion concentration, the less the interference.
pH = 2 to 9 (at 10-3mol/L K+) For reference: Definition of selectivity coefficientThe Nicolsky-Eisenman equation defines the selectivity coefficient where ai represents the activity of an ion other than the target ion denoted by i, and is a value indicating the impact that ion B has on the sensor used to measure ion A. The smaller this value, the better the selectivity with respect to the target ion.“Handbook on Electrochemistry,” 4th ed., Electrochemical Society of Japan, Maruzen, 1985, p. 209 Hence, in practice, the ratio of target ion to interfering ion concentration is very important. Higher concentrations of target ions result in the interfering ions having a smaller effect, and conversely, lower concentrations result in them having a larger effect. Relation page Measurement of Ion What does an ionIon selective electrode (ISE) is an analytical technique used to determine the activity of ions in aqueous solution by measuring the electrical potential.
Which electrode is ionIon-selective electrodes (ISEs) are electroanalytical sensors whose signals depend on the activities of ions in solution and exhibit a certain degree of selectivity for particular ionic species. The operation of classical ISEs is based on direct measurement of a single membrane potential at zero net current.
Which method is used in ion1 Electrodialysis and related technologies. Electrodialysis uses positively and negatively charged membranes and an electrical potential difference to extract ions from aqueous solutions.
What are ionIon-selective electrodes can either be classified according to the membrane material used or the type of electrode body arrangement. Both classifications show that neutral carrier-based liquid membrane microelectrodes represent a very special type of electrode out of a vast variety of sensors.
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