What acid is used to preserve ammonia in a sample?

The appropriate acid used to preserve ammonia in a wastewater sample is sulfuric acid (H2SO4). When preserving samples for ammonia analysis, the addition of sulfuric acid prevents the loss of ammonia through volatilization, which can occur in neutral or alkaline conditions. This stabilization is crucial, as it ensures that the ammonia concentration in the sample remains unchanged over time until analysis can be performed.

Sulfuric acid not only lowers the pH of the sample, making it less conducive to the escape of ammonia gas, but it also acts to convert any ammonium ions (NH4+) in the sample into a form that is more stable for analysis. This preservation method is widely accepted in laboratory protocols for accurate ammonia measurement.

Other acids such as phosphoric acid and hydrochloric acid could potentially alter the chemistry of the sample differently, while acetic acid does not provide effective stabilization for ammonia under typical laboratory conditions. Thus, sulfuric acid is specifically recommended for this purpose in wastewater analysis.