Measurement Techniques; Degassing - Removal Of Bubbles - VWR TIR 200 Mode D'emploi

Measurement techniques

Degassing – removal of bubbles
Note: Do not use with TSK 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
Note:
This procedure can influence the nature of the sample and therefore the turbidity reading.
Type of Method
sample
Samples Addition of a sur-
oversaturated factant
with air
Liquid sam- Use of a partial
ples without vacuum
readily volatile
components
Viscous Use of an ultrasonic
samples bath
Very viscous Heating the sample
samples
20
Description of the
method
Surfactants minimise
the surface tension
of a sample, allowing
entrained gases to
disappear.
A vacuum can be cre-
ated with the help of a
clean, oil-free syringe
or pump fitted onto
a vial.
The vacuum reduces
the atmospheric pres-
sure, so that trapped
air bubbles can be
removed.
The ultrasonic waves
excite the sample,
effectively removing
air bubbles from most
samples.
Heating the sample
makes it less viscous,
air bubbles can disap-
pear more easily.
The sample has to cool
to its original tempera-
ture.
Notes:
Particles in the sample
settle more rapidly, so
the sample must be
swirled before being
measured.
Avoid vigorous shak-
ing as this causes the
surfactant to foam.
Volatile components
can escape from the
sample.
The vacuum may
compound the air bub-
ble problem in viscous
samples.
Ultrasonic waves can
change the particle
size in the sample,
therefore changing the
turbidity.
Volatile components
can disappear from the
sample. The attributes
of suspended particles
change, therefore
changing the turbidity.
VWR ver 1 01/2018