emperature, and pH). In certain cases, such as for BOD, composite samples are routinely
required
by regulatory agencies. Refrigerate composite samples for BOD and nitrite.
Sample carefully to ensure that analytical results represent the actual sample composition.
Important factors affecting results are the presence of suspended matter or turbidity,
the method
chosen for removing a sample from its container, and the physical and chemical changes brought
about by storage or aeration. Detailed procedures are essential when processing (blending,
sieving, filtering) samples to be analyzed for trace consti
tuents, especially metals and organic
compounds. Some determinations can be invalidated by contamination during processing. Treat
each sample individually with regard to the substances to be determined, the amount and nature
of turbidity present, and other
conditions that may influence the results.