2021 Volume 70 Issue 3 Pages 191-197
The proton spin-spin relaxation times (T2) of ion-selective electrode membranes prepared from different solvents were investigated. The potentiometric polymeric membranes based on bis(12-crown-4) as an ionophore for the Na+ ion-selective electrodes were chosen as model ISE membranes. The solvents applied to the preparation of the potentiometric polymeric membranes were tetrahydrofuran (THF), 1,4-dioxane, acetone, methylethylketone (MEK) and chloroform. T2 measurements were performed using the Hahn-Echo, Solid-Echo and Carr-Purcell-Meiboom-Gill (CPMG) pulse sequences. Analyses of the T2 measurements by Hahn-Echo pulse sequences could provide the average T2 values of the whole potentiometric polymeric membranes. The average T2 values will indicate the degree of plasticization for the whole membranes. Moreover, the normalized derivative spectra by T2 measurements of the Solid-Echo and CPMG pulse sequences could visualize the degree of plasticization for such potentiometric polymeric membranes. On the other hand, differences in the solvents were found to affect the electromotive force (EMF) response in the low-concentration region of the Na+ ions and selectivity coefficients for the ISE membranes. These results reveal a relationship of the acquired T2 measurement data with the EMF response and the ion-selectivity for a series of the Na+-ISEs based on bis(12-crown-4). The most plasticized ISE membrane by THF exhibited the best EMF response and ion-selectivity.
