Valinomycin enhances the selectivity of an electrode used to quantitate which ion?

Valinomycin enhances the selectivity of an electrode used to quantitate which ion?

• A. Potassium
• B. Sodium
• C. Calcium
• D. Chloride

Answer: (A)

Valinomycin acts as a potassium ionophore, a molecule that binds potassium ions preferentially and transports them across the membrane of an ion-selective electrode. This selective binding creates a membrane environment where potassium is transferred much more readily than other ions, so the electrode potential becomes dominated by the activity of potassium. The cavity in valinomycin fits K+ best in size and coordination, which is why binding to sodium, calcium, or chloride is much weaker. As a result, the electrode with valinomycin provides a more accurate readout for potassium with minimal interference from Na+, Ca2+, or Cl−, and its response follows the expected Nernstian relationship for a monovalent cation.

Valinomycin acts as a potassium ionophore, a molecule that binds potassium ions preferentially and transports them across the membrane of an ion-selective electrode. This selective binding creates a membrane environment where potassium is transferred much more readily than other ions, so the electrode potential becomes dominated by the activity of potassium. The cavity in valinomycin fits K+ best in size and coordination, which is why binding to sodium, calcium, or chloride is much weaker. As a result, the electrode with valinomycin provides a more accurate readout for potassium with minimal interference from Na+, Ca2+, or Cl−, and its response follows the expected Nernstian relationship for a monovalent cation.