LaMotte COD Plus Colorimeter 1922-EX2 - Manual (Page 9)

CHEMICAL TESTING
n
WATER SAMPLING FOR CHEMICAL ANALYSIS
n 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:
l Sample as frequently as possible.
l Collect a large sample or at least enough to conduct whatever tests are
necessary.
l Make a composite sample for the same sampling area.
l
Handle the sample in such a way as to prevent deterioration or
contamination before the analysis is performed.
l Perform analysis for dissolved gases such as dissolved oxygen, carbon
dioxide, and hydrogen sulfide immediately at the site of sampling. These
factors, as well as samples for pH, cannot be stored for later examination.
l 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.
n 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 flow, 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 fitting screw cap. Rinse the container several times with the sample to be
tested, then immerse the container below the surface until it is filled to
overflowing 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 profile of streams, lakes,
ponds, and reservoirs at specific depths. This type of sampling requires more
sophisticated sampling equipment.
For dissolved oxygen studies, or for tests requiring small sample sizes, a Water
Sampler (LaMotte Code 1060) will serve as a subsurface or in-depth sampler.
COD PLUS COLORIMETER 6/02 9