Sampling and Storage
Collect samples in a clean glass or plastic container. Adjust the
pH to 2 or less with nitric acid (about 2 mL per liter). Preserved
samples can be stored up to six months at room temperature.
Adjust the pH to 4.0-5.0 with 5.0 N sodium hydroxide before
analysis. Correct the test result for volume additions; see
Correction for Volume Additions in Section 1.