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SECTION 3, continued
3.2.4 Removing Bubbles (Degassing)
Before measurement, removing air and other trapped gasses from the
sample is strongly recommended, even if bubbles are not visible. Four
degassing methods are commonly used:
• Applying a partial vacuum.
• Adding a surfactant.
• Using an ultrasonic bath.
• Heating the sample.
In some cases, more than one method may be necessary for effective
bubble removal. For example, use of both a surfactant and ultrasonic
bath may be necessary for some severe conditions. Use care with these
techniques. If misused, sample turbidity can be altered.
Letting the sample stand for a period of time to remove air bubbles is
not recommended. Particulates that cause turbidity may settle and the
sample temperature may change, resulting in measurements not
representative of the original turbidity.
3.2.4.1 Application of a Partial Vacuum
The vacuum lowers the atmospheric pressure, allowing trapped bubbles
to escape into the air above the sample. Vacuum works well with
non-viscous samples (such as water) that do not contain volatile
components. Applying vacuum to viscous, volatile samples (paint
resins) may cause the volatile components to come out of solution and
aggravate the bubble problem.
To apply a vacuum, use a sample degassing kit equivalent to
Cat No. 43975-00 (Degassing Kit) or 43975-10 (Degassing and
Filtration Kit). These kits contain a syringe and rubber stopper for
vacuum degassing. An electric or hand-operated pump equivalent to
Cat. No. 14283-00 may also be used.
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