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• Use of an ultrasonic bath;
• Heating the sample.
Sometimes it is necessary to combine two or more methods for efficient air bubble removal.
Note
: Each method can alter the sample turbidity, if misused, so they have to be used with caution.
APPLICATION OF VACUUM
Vacuum works by decreasing the atmospheric pressure. The bubbles from the solution come out to
the surface. Application of vacuum is a very simple procedure andany vacuum can be used. The
simplest equipment is a syringe and a rubber stopper.
Notes
: • Pay attention that the vacuum equipment be clean and oil-free.
• It is not recommended to apply vacuum to a viscous sample that contains volatile
components. The vacuum can disrupt the volatile components and increase the bubbles
in the sample.
ADDITION OF SURFACTANT
Surfactant changes the surface tension of the water. This causes the bubbles to be released from the
sample. This method is effective for samples that are supersaturated with air.
The procedure consists in the addition of a drop of surfactant in the cuvette before adding the sample
to be analyzed.
A common surfactant used for degassing is Triton X-100.
Warning
: Changing the surface tension will cause a rapid settling of particles that cause turbidity.
To avoid this problem, analyze the sample as soon as possible.
Do not shake the sample vigorously because the surfactant may foam. Always rinse the cuvette before
adding a new sample to avoid surfactant accumulation.
Surfactant contribution to the turbidity readings is negligible.
Note
: Surfactant addition should be used for degassing only when other methods are ineffective.
USE OF AN ULTRASONIC BATH
The ultrasonic waves are very effective in removing air bubbles from samples. However, ultrasonic
waves should be used with care because they can alter the samples turbidity characteristics, by
modifying the shape and size of particles which cause turbidity. The ultrasonic waves can also break
the existing air bubbles, leading to a complication in the degassing process.
In order to avoid excess application of the ultrasonic waves use the ultrasonic bath until all visible air
bubbles are removed, and then measure the turbidity. This is the most used procedure for degassing.
If you are not sure that all air bubbles were removed, apply ultrasonic waves again for a short period
of time and then measure the turbidity. Repeat this procedure until the turbidity is increasing instead
of decreasing, sign that turbidity of the sample was altered.
In order to degas a sample, fill a clean cuvette with sample and immerse it (1/2 to 2/3 immersed)
in an ultrasonic bath. Follow the degassing procedure described above. Only after the degassing
procedure is finished the cuvette can be capped.
