Spectroscopic in Situ Imaging of Acid Coextraction Processes in Solvent Polymeric Ion-Selective Electrode and Optode Membranes

Abstract

Time-dependent processes induced by acidic solutions in solvent polymeric membranes with a H + -selective chromoionophore are studied in a spectropotentiometric setup. They are important for understanding the response time of anion-selective optodes and the response of H + -selective electrodes at low pH when anion interference is potential determining. The extent of anion−proton coextraction is characterized with extraction experiments on thin optical films (optodes) containing the same components and described by theory. Imaging experiments indicate rapid diffusion processes and unusual nonlinear steady-state concentration profiles that are explained by parallel extraction of undissociated acid into the membrane. Long-term potential drifts of the respective electrode are detected and related to the diffusion processes.