Which method is enzymatic (GLDH) for ammonia determination?

• A. Potentiometric ISE
• B. Nesslerization
• C. Enzymatic GLDH
• D. Berthelot

Answer: (C)

Ammonia can be measured by several approaches, and the enzymatic option uses the enzyme glutamate dehydrogenase (GLDH). In this method, ammonia reacts with α-ketoglutarate in the presence of GLDH and NADH to form L-glutamate and NAD+. The key readout is the decrease in NADH as it is oxidized to NAD+, which can be tracked spectrophotometrically at 340 nm. The rate or amount of NADH consumed is proportional to the ammonia concentration, providing a specific enzymatic measurement.

The other common approaches are chemical or electrochemical rather than enzymatic. Potentiometric ISE detects ammonia activity directly with an ion-selective electrode, not using an enzyme. Nesslerization uses Nessler’s reagent to produce a color change in the presence of ammonia, a chemical method. The Berthelot (indophenol) method also relies on a chemical reaction to form a colored complex. Therefore, the method that is enzymatic is the GLDH-based approach.