LaMotte SMART3 Colorimeter - Manual (Page 11)

CHEMICAL TESTING
 WATER SAMPLING FOR CHEMICAL ANALYSIS
Taking Representative Samples
The underlying factor to be considered for any type of water sampling is whether
or not the sample is truly representative of the source. To properly collect a
representative sample:
• Sample as frequently as possible.
• Collect a large sample or at least enough to conduct whatever tests are
necessary.
• Make a composite sample for the same sampling area.
• Handle the sample in such a way as to prevent deterioration or
contamination before the analysis is performed.
• Perform analysis for dissolved gases such as dissolved oxygen, carbon
dioxide, and hydrogen sulfi de immediately at the site of sampling. Samples
for testing these factors, as well as samples for pH, cannot be stored for
later examination.
• Make a list of conditions or observations which may affect the sample.
Other considerations for taking representative samples are dependent
upon the source of the sample. Taking samples from surface waters
involves different considerations than taking samples from impounded and
sub-surface waters.
Sampling of Open Water Systems
Surface waters, such as those found in streams and rivers, are usually well
mixed. The sample should be taken downstream from any tributary, industrial
or sewage pollution source. For comparison purposes samples may be taken
upstream and at the source of the pollution before mixing.
In ponds, lakes, and reservoirs with restricted fl ow, it is necessary to collect a
number of samples in a cross section of the body of water, and where possible
composite samples should be made to ensure representative samples.
To collect samples from surface waters, select a suitable plastic container with
a tight fi tting screw cap. Rinse the container several times with the sample
to be tested, then immerse the container below the surface until it is fi lled to
overfl owing and replace the cap. If the sample is not to be tested immediately,
pour a small part of the sample out and reseal. This will allow for any expansion.
Any condition which might affect the sample should be listed.
Sub-surface sampling is required to obtain a vertical profi le of streams, lakes,
ponds, and reservoirs at specifi c depths. This type of sampling requires more
sophisticated sampling equipment.
For dissolved oxygen studies, or for tests requiring small sample sizes, a Water
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