The most practical and reliable method of preservation in the field is refrigeration. Equipment is usually available and it doesn't interfere with analysis. Putting samples in ice and keeping them there until they are submitted to the laboratory will preserve them well enough for most tests. 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.