Which of these substances is used to enhance the selectivity for potassium in ion-selective electrodes?

Valinomycin is a well-known ionophore that specifically binds to potassium ions (K+), enhancing the selectivity of ion-selective electrodes (ISEs) for this particular ion. It facilitates the transport of potassium across a membrane by forming a stable complex with the ion. This selectivity is crucial in various analytical applications, such as measuring potassium levels in clinical samples, because it minimizes interference from other cations that may be present in the solution.

The ability of valinomycin to selectively bind potassium ions is a key feature that makes it suitable for use in ion-selective electrodes. Its structure allows it to fit potently with K+ ions due to the ion's size and charge, leading to relatively high sensitivity and specificity.

In contrast, the other substances mentioned have different roles or properties and do not enhance the selectivity for potassium in the same effective manner. Chloride, for instance, does not specifically enhance potassium selectivity; instead, it may contribute to other analytical responses but lacks the targeted specificity that valinomycin provides. Similarly, a calcium ionophore is more related to calcium ions and would not aid in the selective measurement of potassium ions. Benzyl alcohol is often used as a solvent or in various chemical applications