In the 3 diazo reagents setup, what is Diazo A composition?

• A. 0.1% sulfanilic acid in HCl
• B. 0.5% sodium nitrite
• C. 1.5% HCl
• D. 0.1% nitrite in water

Answer: (A)

Diazotization in this nitrite-detection setup requires the aromatic amine component in a strongly acidic medium to form the diazonium ion. Providing that amine, in this case sulfanilic acid dissolved in hydrochloric acid, is what makes the first reagent effective. So the Diazo A reagent is 0.1% sulfanilic acid in HCl. The other options don’t provide the necessary amine: sodium nitrite supplies nitrite, not the aryl amine; plain hydrochloric acid or nitrite in water lacks the amine needed to form the diazonium salt. Once the diazonium ion forms, it can couple with the next reagent to produce the colored product detected in the test.