Which statement is false regarding ion-selective electrode analysis of sodium?

Which statement is false regarding ion-selective electrode analysis of sodium?

• A. It uses a glass membrane
• B. Errors occur from protein buildup on the membrane
• C. Membrane coated with valinomycin
• D. The analysis is based on potentiometry

Answer: (C)

Ion-selective electrode analysis for sodium relies on a membrane that responds specifically to sodium ions and produces a potential that reflects Na+ activity. The classic sodium electrode uses a glass membrane whose surface interacts with Na+ to generate a potential that changes with sodium activity, in line with the Nernst equation. In practice, proteins or other substances can foul the membrane, altering its surface properties and hindering ion transfer, which leads to measurement errors. The measurement in this method is potentiometric, meaning it detects a voltage difference rather than driving current. Valinomycin, however, is a potassium-selective ionophore; when used in a membrane it confers high selectivity for K+ over Na+. Therefore a membrane coated with valinomycin would not be appropriate for sodium analysis, making that statement the false one.

Ion-selective electrode analysis for sodium relies on a membrane that responds specifically to sodium ions and produces a potential that reflects Na+ activity. The classic sodium electrode uses a glass membrane whose surface interacts with Na+ to generate a potential that changes with sodium activity, in line with the Nernst equation. In practice, proteins or other substances can foul the membrane, altering its surface properties and hindering ion transfer, which leads to measurement errors. The measurement in this method is potentiometric, meaning it detects a voltage difference rather than driving current. Valinomycin, however, is a potassium-selective ionophore; when used in a membrane it confers high selectivity for K+ over Na+. Therefore a membrane coated with valinomycin would not be appropriate for sodium analysis, making that statement the false one.