Coulometry is still used for chloride determinations in body fluids, such as sweat. Which fluid is commonly analyzed by this method?

• A. Chloride in Sweat
• B. The pH in Saliva
• C. Bicarbonate in Urine
• D. Ammonia in Plasma

Answer: (A)

Coulometry for chloride is a direct way to quantify chloride concentration by measuring the charge required to drive the chemical reaction that releases or binds chloride at an electrode. This method is especially used with sweat because elevated sweat chloride is a key diagnostic marker for cystic fibrosis. Sweat is collected after stimulating the glands, and the chloride level is determined by the amount of electricity needed in the coulometric reaction, giving a precise measurement of chloride content.

The other fluids listed aren’t typically analyzed by this chloride-focused coulometric method. pH in saliva is usually read with a pH electrode, bicarbonate in urine is determined by titration or enzymatic/other methods, and ammonia in plasma is measured with ammonia-specific enzymatic or conductivity-based assays.