Camlab CW8200, Manual

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2.3.8 Measurement techniques
2.3.8.1 Degassing - Removal of Bubbles
If the Turbidity is low it is important to remove air bubbles from the sample using one,
or a combination of the following methods:
Addition of a surfactant
Application of a partial vacuum
Application of heat
Use of an ultrasonic bath
This procedure can influence the nature of the sample and therefore the turbidity reading.
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Type of
sample Method Description of the
method Notes:
Samples that
are oversatu-
rated with air Addition of a surf-
actant Surfactants minimize
the surface tension
of a sample, allowing
entrained gases to
disappear. Particles in the sample
settle more rapidly, so
the sample must be
swirled before being
measured. Vigorous
shaking causes the
surfactant to foam.
Liquid sam-
ples without
readily volatile
components Use of a particle
vacuum A vacuum can be crea-
ted with the help of a
clean, oil-free syringe
or pump fitted onto
the cuvette.
The vacuum reduces
the atmospheric pres-
sure, so that trapped
air bubbles can be
removed. Volatile components
can escape from the
sample.
The vacuum may com-
pound the air bubble
problem in viscous
samples.
Viscous
samples Use of an ultrasonic
bath The ultrasonic waves
excite the sample,
effectively remove air
bubbles from most
samples. Ultrasonic waves can
change the particles
size in the sample,
therefore changing the
turbidity.
Very viscous
samples Heating the sample Heating the sample
makes it less viscous,
air bubbles can disap-
pear more easily.
The sample has to cool
to its original tempe-
rature. Volatile components
can disappear from the
sample. The attributes
of suspended particles
change, therefore
changing the turbidity.