Environmental Engineering Reference
In-Depth Information
3.4 Sampling with different flow rates and material composition
(source: Schwedt G (2007) Taschenatlas der Analytik. Wiley-VCH,
Weinheim, Germany; Figure E on p.19; copyright Wiley-VCH Verlag
GmbH & Co. KGaA; reproduced with permission).
least one sample should be drawn from every phase. These samples can then
be mixed together according to the quantity of the phases. If the material is
very inhomogeneous and no phases can be located, samples should be
drawn from different locations and depths of the material. They can also be
put together as a mixed sample.
For solid material, a representative sample can be obtained using the
following procedure. With a spade or a sampling device, a large sample is
taken from the material. This large sample is spread onto a clean surface
and then mixed well. A cross is then drawn through the middle of the spread
sample and two opposite quarters are removed. The remaining two quarters
are spread and mixed again and again a cross is drawn and two quarters
removed. This process is repeated until the required amount of sample is
obtained.
For liquid material, the liquid has to be stirred well before sampling. The
sample bottle should then be submersed into the liquid for sampling. If a
sampling valve is used, the first material leaving the valve should be rejected
to allow cleaning of the sampling valve. If a sample is taken from a pipe
where the material passes at different flow rates and with different
composition, a sample proportional to flow rate or volume can be taken
(Fig. 3.4). Automatic sampling devices can be used for this purpose. In
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