Preservatives used to reduce changes in the sample 1 . Proper preservation can only retard the chemical and biological changes in the sample. Complete preservation is impossible in most cases. Changes occur rapidly once the waste has been collected. Biological action involving nitrogen and phosphorus cycles are the most notable changes in waste samples.
Organic nitrogen is released as ammonia nitrogen when bacteria decompose organic matter.
Ammonia is lost as a gas or converted to nitrites, which are rapidly oxidized to nitrates by bacteria. Nitrates can be reduced back to ammonia by bacterial reduction. This cycle continues unless retarded by a bacterial inhibitor. The nitrogen balance can be held in check for a maximum of seven days by adding sulfuric acid and refrigerating the sample. In determining phosphorus content, preservation is not necessary if total phosphorus is to be determined.