In determining phosphorus content, preservation is not necessary if total phosphorus is to be determined. Organic phosphorus is converted to orthophosphate by bacterial decomposition. This refrigeration will maintain biochemical oxygen demand. Certain ions may change chemically in a waste sample. Metal ions may be precipitated as insoluble salts or absorbed onto the wall of the collection bottle, while other ions may change form.
Preservation is accomplished by refrigerating or by adding nitric acid.
There are no practical methods of preserving these. Analyses for them should be performed at the collection site. Recommended preservatives and maximum holding periods for most determinations made on wastes and waste waters are summarized in Table 2. Know which specific analyses are to be made on the sample. Collect representative samples.