Which method for urea determination uses diacetyl monoxime (DAM) to produce a yellow diazine?

• A. Direct Chemical/Fearon
• B. Indirect Enzymatic
• C. Jaffe method
• D. Kjeldahl method

Answer: (A)

This question tests recognizing a colorimetric, direct chemical method for measuring urea that uses diacetyl monoxime to form a yellow diazine. In this approach, urea reacts under strongly acidic conditions with diacetyl monoxime (often with a catalyst such as ferric ions) to produce a yellow diazine complex. The intensity of that yellow color is proportional to the urea concentration and is read spectrophotometrically. This distinguishes it from enzymatic methods (which rely on urease to release ammonia), the Jaffe reaction (which detects creatinine), and Kjeldahl digestion (which measures total nitrogen). So the reaction involving diacetyl monoxime and the resulting yellow diazine is the hallmark of this direct chemical urea determination method.