Improved Separate Solution Method for Determination of Low Selectivity Coefficients

Abstract

Simple, fast, and theoretically substantiated experimental method for determination of improved selectivity coefficients is proposed. The method is based on the well-known fact that low selectivity coefficients determined by the separate solution method (SSM) are time-dependent and, upon our finding, this dependence is a well-defined linear function of time raised to the certain negative power. In particular, the selectivity coefficients obtained for equally charged primary and foreign ions by SSM linearly depend on time to the minus one-fourth. It was found that extrapolation of experimental data using this function to the intersection with Y axes gives reliable values of rather low selectivity coefficients (down to n × 10(-7)), which strongly differ from those measured using SSM and correspond well with the values obtained using the modified separate solution method (MSSM) proposed by Bakker. At the same time, the new method is free of one very essential limitation inherent to MSSM, namely, it is applicable after the conditioning of electrodes in the primary ion solution and can be repeated many times.

Generalized Diffusion Parameter: Main Factors of Influence and Application for Estimation of Selectivity Coefficients for Highly Selective Electrodes

“…The estimated values of the selectivity coefficients K A,B pot lim , in contrast to ones experimentally obtained by SSM, are practically independent of the concentration level of the foreign ion and are very close to unbiased values obtained by Bakker’s method 14. It should be noticed that the proposed method is even more effective in comparison with the one described in 29, as it never gives absurd results.…”

“…For very low K A,B pot lim values the inaccuracy in its determination can exceed 100 % leading to absurd negative values. It was experimentally found that the lowest selectivity coefficients, which can be determined by this method, are about n×10 −7 29.…”

“…We have recently proposed an improved separate solution method for the estimation of low selectivity coefficients 29. According to this method, rather low selectivity coefficients close to unbiased ones and differing from those obtained by separate solution method about 10 or even more times can be determined as the intersection with Y‐axis of the linear dependence of the selectivity coefficients on time raised to the certain negative power.…”

Solid-contact lead(II) ion-selective electrodes for potentiometric determination of lead(II) in presence of high concentrations of Na(I), Cu(II), Cd(II), Zn(II), Ca(II) and Mg(II)

“…For many years that parameter, however, was not uniformly determined as diverse protocols and methods were applied, many of which resulted in the determination of biased selectivity coefficient. In order to compare and verify different ionophores, currently there is a requirement for reporting unbiased selectivity coefficients [6,7]. Therefore, a common methodology, the separate solution method (SSM) and the fixed interference method (FIM) for ISEs selectivity determination were adapted [5,8].…”

Unbiased Selectivity Coefficients of Potentiometric Sensors Using Thin Membrane Layers

“…Several approaches have been reported in the literature to solve this problem, including the so‐called modified separate solution method (MSSM) [7c], which is based on preconditioning the membrane with a discriminated ion instead of the analyte ion, and the extrapolation of the time‐dependent electrode responses in a solution of interfering ions [7d,e]. An obvious limitation of the first method is that it can no longer be used after first contact with primary ions.…”