Selectivity studies on liquid membrane, ion-selective electrodes

Abstract

A series of anion-selective electrodes of the liquid membrane type has been rigorously examined with respect to selectivity characteristics using three different experimental methods. This evaluation gives, for the first time, an understanding of how selectivity ratios depend on concentration levels and other variables and yields a recommended procedure for the consistent numerical determination of selectivity ratios. The resulting selectivity data are examined in terms of a theory of liquid membrane electrodes.Since the introduction of the liquid membrane electrode selective for calcium in 1967 (/), many new electrodes of this type with selective response to both cations and anions have become available. Evaluative studies (2-6) of these electrodes have demonstrated the Nernstian response and dynamic range of these electrodes, but have also revealed their gradual loss of selectivity and general deterioration with time under extended use.Generally speaking, the selectivities of liquid membrane electrodes for the ion of primary interest with respect to common interfering ions are only moderate (7-8). Never-theles^gfhe electrodes have been successfully employed analytical! < direct potentiometry or potentiometric titrations (3, 5, c , 9-13) under suitable conditions where interfering ions are absent or present in low concentrations.If the full usefulness of ion-selective electrodes of the liquid membrane type is to be realized, reliable methods of establishing their selectivity characteristics and accurate numerical data on selectivities must be made available. Unfortunately, there is little agreement in the literature regarding optimal methods of determining selectivities or, even, on the selectivity ratios of a specified electrode. In part, this difficulty arises from a lack of systematic study and from the tendency to report selectivities under a single, and often arbitrary, set of conditions.In this paper we, therefore, set out to evaluate the selectivities of a series of anion-selective, liquid membrane electrodes

Selenite-Selective Membrane Electrodes Based on Ion Exchangers and Application to Anodic Slime

“…For this purpose, the mixed solution method 15 is preferred, as it usually corresponds more closely to the situation in samples. In this method, solutions are prepared with a constant activity of the main ion and varying activity of interfering ion.…”

“…For this purpose, about 1.0 g of anodic slime samples are dissolved either in HCl + HNO3 (1 + 3) or in HNO3. 15 Acids are then evaporated nearly to dryness and then the sample is diluted into 50.0 ml. An aliquot of 0.05 ml is taken, 5.0 ml 0.1 M NH3-NH4Cl buffer (pH=8) and 1 ml of 1 M NaNO3 is added and the mixture is diluted into 10.0 ml.…”

Potentiometrie Carbon Paste Sensors for Lead(II) Based on Dithiodibenzoic and Mercaptobenzoic Aeids

“…The selectivity coefficients (KPb,M) of the proposed carbon paste electrodes towards different cationic species (M n+ ) were determined by the Mixed Solution Method (MSM) 31 and…”

Sulfate-selective Electrode Based on a Complex of Copper

“…The selectivity of the proposed sulfate ion selective electrode over other anions (A -) was important; their potential responses were investigated in the presence of a wide variety of interfering foreign anions using the mixed solution method (MSM). 31,32 Potentiometric selectivity coefficients (K pot sul,A -) describing the preference of the membrane for an interfering ion A -relative to SO4 2-were determined by the fixed interference method (FIM). The selectivity coefficients for various anions were evaluated by the mixed solution method with a fixed concentration of interferent (0.10 M), and varying amounts of SO4 2-concentrations.…”