Determination of the ion-exchange capacity of anion-selective membranes

• Three methods of determination of IEC of anion-selective membranes compared.
• Accuracy of the individual methods discussed.
• Impact of functional group structure determined.
• Recommendations on the appropriate method selection provided.

The ion-exchange capacity (IEC) is one of the fundamental characteristics of ion-selective membranes. So far, the most widely used technique for IEC determination is titration. However, this method is very sensitive to experimental conditions, especially when anion-selective membranes are treated. This study compares three different methods of IEC determination of anion-selective membranes, namely titration of Cl− ions, spectrophotometric determination of NO3− ions and determination of OH− ions exchanged by the membrane for different counter-ions by ion-selective electrode. Differences of up to 24% were observed, a discrepancy mainly caused by the presence of weakly basic functional groups in the membrane. With respect to the utilization of this type of material as an alkaline solid polymer electrolyte, it is important to distinguish between the types of functional groups.