Aqualytic AL400T-WL, Instruction Manual, Page: 21 / 32

21
AL400T-WL_2a 07/2011
2.3.3 Measurement techniques
2.3.3.1 Degassing – Removal of Bubbles
Attention: Do not use with secondary standards!
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.
Type of
sample Method Description of the
method Notes:
Samples that
are oversatu-
rated with air Addition of a
surfactant Surfactants minimise
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
samples
without rea-
dily volatile
components Use of a partial
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 removing
air bubbles from most
samples. Ultrasonic waves can
change the particle
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.