Studies of ion selective solvent polymeric membranes by X-ray photoelectron spectroscopy and time-of-flight static secondary ion mass spectroscopy

X-ray photoelectron spectroscopy and time-of-flight static secondary ion mass spectroscopy were successfully applied in the surface characterization of plasticized PVC-based ion-selective electrode membranes, as well as of the starting material, PVC. Carboxylic and alkyl sulfate groups were identified on PVC and were proposed to represent the intrinsic ionic sites of the membranes. Enrichment of both the plasticizer and the ionophore was detected on the surface of the plasticized membranes, cast from THF solutions. The extent of enrichment was higher at the membrane-to-air side than at the membrane-to-mold side. Poly(dimethylsiloxane) was found as an unexpected impurity (originating from the PVC powder). This compound was also substantially enriched at the surfaces of the membranes. Surface composition of the plasticized PVC membrane did not change after 2.5 h of soaking in water.