How long can an ammonia nitrogen sample be preserved at 4 degrees C on sulfuric acid?

The preservation of ammonia nitrogen samples in sulfuric acid at a temperature of 4 degrees Celsius is an important consideration for maintaining the integrity of the sample for analysis. When sulfuric acid is used to acidify and preserve the sample, it effectively prevents the conversion of ammonia to other nitrogen forms, allowing for accurate measurement of ammonia levels.

The correct duration for which the sample can be preserved under these conditions is 28 days. This preservation window is crucial for ensuring that the ammonia concentration remains stable and representative of the original sample. After 28 days, the ammonia concentration can begin to change due to microbial activity and chemical reactions, making the results unreliable.

This preservation protocol is established to help operators maintain consistent and reliable results when sampling wastewater or other water sources for ammonia nitrogen, which is a critical parameter in wastewater treatment monitoring.