What causes a "response" error from an ion-selective electrode for sodium when measuring serum?

A "response" error from an ion-selective electrode (ISE) for sodium primarily occurs when there is an impediment to the electrode's ability to detect the ion concentration accurately. In the case of option B, protein coating the ion-selective membrane can inhibit the electrode's capacity to respond to sodium ions appropriately. The ion-selective membrane is designed to selectively allow sodium ions to pass through and be measured; however, if the membrane becomes coated with proteins, this can create a barrier that prevents sodium ions from reaching the membrane effectively. As a result, the electrode may not generate a response that accurately reflects the true sodium concentration in the serum sample.

This issue is distinct from the other options, which may lead to different types of errors but do not directly relate to the fundamental operational principle of the ion-selective electrode. Interference from other electrolytes could cause inaccurate readings, but this does not constitute a response error specific to sodium measurement. An overrange in sodium concentration would typically lead to saturation of the electrode response rather than a malfunction due to membrane issues. Protein binding to sodium ions could theoretically affect readings but typically leads to altered free sodium concentration measurement rather than a direct membrane response error, making coating a more precise elucidation of the problem presented in