SAMPLING
Samples used for the determination of phosphorus can be either grab or composite. The type of sample used will depend on the monitoring requirements, plant operating procedures and the testing and sample storage capabilities of individual plants. Samples should be collected from well-mixed areas in the process flow so that they are representative of the total flow
SAMPLE PRESERVATION
If Total Phosphorus is the only determination to be made, acidify the sample to less than pH 2 with sulfuric acid and cool to 4°C. Acidified and cooled samples may be held for up to 28 days. If the test is run immediately, no preservative is required.