What is the preservation for Ammonia samples?

• A. Analyze ASAP or add H2SO4 to pH<2, cool, <=6C
• B. No preservation; store 28 days
• C. Cool 4C; 7 days
• D. Freeze; 60 days

Answer: (A)

Preserving ammonia samples hinges on preventing loss of ammonia as a volatile gas and keeping the chemical form stable. Ammonia in water can readily volatilize as NH3 if the sample isn’t kept in the right conditions. By acidifying the sample to pH below 2, the ammonia is shifted toward the ammonium form (NH4+), which is far less volatile. Keeping the sample cold (at or below 6°C) slows any biological or chemical changes that could alter the ammonia concentration. That’s why the best practice is to analyze the sample as soon as possible, or, if immediate analysis isn’t feasible, preserve by adding sulfuric acid to lower the pH to below 2 and keep the sample cooled.

The other options aren’t appropriate because they either delay analysis too long or omit essential preservation steps. Simply storing without preservation for 28 days allows substantial ammonia loss; cooling alone without acidification doesn’t prevent volatilization, and freezing for an extended period isn’t the standard or reliable approach for preserving ammonia and can complicate analysis.