Hydrogen ion concentration in blood is determined using which type of electrode?

• A. Silver
• B. Glass
• C. Platinum
• D. Platinum-Lactate

Answer: (B)

Measuring hydrogen ion activity (pH) in blood uses a glass electrode because its membrane responds selectively to hydrogen ions. The thin glass bulb surface exchanges H+ with the solution, creating an electrical potential at the glass–electrolyte interface that depends on the hydrogen ion activity in the sample. This potential is measured against a stable reference electrode, and the resulting signal is translated into pH, typically about 59 mV per pH unit at room temperature. Since pH is a log measure of hydrogen ion activity, the glass electrode provides a direct way to determine hydrogen ion concentration indirectly through pH.

Other electrodes aren’t suited for this purpose: a silver electrode is commonly used as a reference or in redox measurements, not to sense H+ directly; a platinum electrode is inert and used for redox potentials rather than selective hydrogen ion sensing; and a platinum-lactate electrode is designed for detecting lactate, not hydrogen ion activity.