The interpretation of non-ideal calibrations of ion-selective electrodes

Abstract

Procedures are developed for analyrlng non-Nernstlan responses of ion-selective electrodes arising from the followlng causes: (I) the presence of determlnand In reagents added to a sample solution, (il) the presence of lnterferlng species, (Ill) the solubility of the material of the electrode itself.Secondary effects due to the actlon of complexlng agents or the establishment of steady-state rather than equlllbrium condltlons are also consldered. The theory Is rlgorously developed for several types of solld-state electrode, and is tentatively applied to liquid membrane electrodes also. Applicatlon of the correct procedure results In a llnear graph wlth an intercept that can be used to calculate the reagent blank and/or the level of interference and a slope with a value characterlstlc of the type of non-Ideal behavior, provlded that the electrode is operatlng reversibly and has a mechanlsm conformlng to the models discussed. Practical examples are taken, involvlng glass, llquld lon-exchange, and solid-state electrodes.

Non-linear dissolution mechanisms of sodium calcium phosphate glasses as a function of pH in various aqueous media

“…Solution pH was measured using a Hanna HI 4222 pH meter with HI 1131B pH electrode and three point calibration. Ca 2+ ion concentration was measured using an ISE (ion selective electrode -Sentek 361-75 Calcium Combination ISE), calibrated using a modified Nernst equation [25] with standard solutions diluted with DI water from a 0.1 mol L -1 calcium standard (Hanna HI 4004-01). To measure glass disc mass during dissolution, discs were removed from solution, rinsed with DI water, dabbed dry, and weighed (using a Sartorius BP61 balance with internal calibration, d = 0.1 mg), before being returned to the solution for further dissolution.…”

“…The average of these values was used to fit the calibration curve. A modified Nernst equation was fitted to account for reagent blank determinand as well as interference at low concentration, which occurs with all electrodes [25]. Calibration was repeated before measurement of each new timepoint, and the electrode was cleaned if the slope (S 1 ) deviated significantly (>2 mV) from the theoretical value of 29.6 mV/decade at 25℃.…”

Data analysis for concentration measurements in the nonlinear response region of ion-selective electrodes

“…Methods Based on the Nonideal Behavior of the Electrodes. For this class of methods the potential functions discussed by Midgley (3) and Parthasarathy et al (4) can be used to determine the cause of the nonlinear behavior. Once a proper potential function has been found, it is used to determine the concentrations.…”

“…Among the few published methods for doing this are the graphical calibration methods and the methods by Midgley (3), Parthasarathy et al (4), and Frazer et al (5) of inherent errors associated with nonlinear graphical interpolation, the graphical methods are not very accurate. The methods by Midgley and Parthasarathy et al involve assumptions about the electrode slope and standard electrode potental which lead to error in concentration measurements.…”

The evolution of the structure and mechanical properties of fully bioresorbable polymer-glass composites during degradation

“…Nernst equation [24] with standard solutions diluted with deionised water from a 0.1 mol L -1 calcium standard (Hanna HI 4004-01). PBS alone was used as a control for pH and Ca 2+ ion measurements.…”