Proton spin relaxation study with pulsed NMR on the plasticization of Na+ ion-selective electrode membranes prepared from PVCs with different degrees of polymerization†
The proton spin–spin relaxation times (T2) of ion-selective electrode membranes with differences in the polymerization degree of the incorporated poly(vinyl chloride) (PVC) polymers were investigated. T2 measurements were performed using Hahn-Echo, Solid-Echo and Carr–Purcell-Meiboom-Gill (CPMG) pulse sequences. Analyses of the T2 measurements by Hahn-Echo pulse sequences could realize the estimation of the homogeneity and compatibility for a series of ion-selective electrode membranes and reveal a relationship with the electromotive force (EMF) response in the low-concentration region of the Na+ ions. On the other hand, the normalized derivative spectra from T2 measurements by Solid-Echo and CPMG pulse sequences could approximately visualize the degree of plasticization for such potentiometric polymeric membranes. Moreover, differences in the polymerization degrees of the incorporated PVCs were scarcely found to affect the selectivity coefficients of the Na+-ISEs based on bis(12-crown-4).