Coupled diffusion/adsorption model for response of precipitate-based iodide-selective electrodes to primary-ion activity steps

Switched wall-jet streams of Iodide solutions Impinging on Agl-based Ion-selective electrodes (ISEs) give potential responses after the first 20 ms. The responses to Iodide activity steps of constant ratio a (flnal)/a (Initial) are highly dependent on the starting activity. This Is contrary to most present theories of ISE response, particularly those describing reversible surface Ion exchange controlled by diffusion to a surface or first-order reaction kinetics. Experimentally, diffusion Is Involved over all concentration ranges but Is coupled with some surface adsorption Isotherm. At low activities, steps up or down are slower than diffusion because of the need to form or remove some of the adsorbed layer. At high activities, step responses approach pure diffusion control, since adsorption Is nearly saturated. Dependence on the starting activity requires a nonlinear adsorption Isotherm, which Is consistent with adsorption data showing logarithmic dependence of surface Ion concentration on bathing activity. Experimentally, rate-controlling dlssolutlon/preclpltatlon processes are not likely. © 1991, American Chemical Society. All rights reserved

Response time studies on neutral carrier ion-selective membrane electrodes

In order to study the parameters affecting the dynamic characteristics of neutral carrier ion-selective electrodes, the response time curves of vallnomycin-based potassium electrodes with different membrane compositions were recorded. The effect of membrane matrix, incorporated ion-exchange sites, and carrier concentration has been investigated thoroughly. The experimental results have been compared with theoretical models. © 1978, American Chemical Society. All rights reserved