1-50
taken near the center of the vessel or duct and below the surface. Use
only clean containers (bottles, beakers) for collecting samples. Rinse
the container several times first with the water to be sampled.
Take samples as closely as possible to the source of the supply to
minimize the effects of a distribution system. Allow the water to run for
sufficient time to flush the system, and the sample container should be
filled slowly with a gentle stream to avoid turbulence and air bubbles.
Collect water samples from wells after the pump has run long enough to
deliver water representative of the ground water feeding the well.
It is difficult to obtain a truly representative sample when collecting
surface water samples. Best results are obtained by running a series of
tests with samples taken from several locations and depths at different
times. Results then can be used to establish patterns applicable to that
particular body of water.
Generally, as little time as possible should elapse between collecting the
sample and making the analysis.
Depending on the nature of the test, special precautions in handling the
sample also may be necessary to prevent natural interferences such as
organic growth or loss or gain of dissolved gases. Sample preservatives
and storage techniques are described in each procedure for sample held
for later testing.
Acid Washing Bottles
A procedure may suggest acid-washing the sample bottles to minimize
the effect of interferences. This is accomplished by using a detergent to
clean the glassware or plastic-ware, rinsing with tap water, rinsing with a
1:1 Hydrochloric Acid Solution or 1:1 Nitric Acid Solution, rinsing with
deionized water. This may require successive rinses, up to 12-15 may be
necessary if chromium is being determined. Air dry. The nitric acid
rinse also is important if lead is being determined.
Chromic acid or chromium-free substitutes may be used to remove
organic deposits from glass containers, but rinse containers thoroughly
with water to remove traces of chromium.
Glassware for phosphate determinations should be washed with
phosphate-free detergents and acid-washed with 1:1 HC1. This
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