Qsonica Sonicator Q700 Operation Manual - page 23
Rev. 9-16
23
Techniques for Optimizing Results
Probe Depth
Immerse the probe tip 1.5 times the tip diameter into the solution, without touching the bottom. For
example, the ½” horn should be immersed at least ¾” below the liquid surface. Immersion depth
must be sufficient to prevent foaming and allow the sample to mix well. If the probe is too deep it
will sonicate against the bottom of the vessel and not promote good mixing to affect the sample
near the top of the vessel.
Foaming and Aerosoling
Aerosoling and foaming generally occur when the tip is not immersed deep enough into the solution
or the amplitude setting is too high. Lowering the tip in the solution, decreasing power, and
reducing solution temperature will prevent foaming. Lowering the power and increasing sonication
time will usually reduce aerosoling; in severe cases, use an aerosol cap or sealed atmosphere
treatment chamber. In organic materials, protein release from cell material acts like a wetting
agent and tends to promote foaming. For severe foaming:
Once foaming occurs, shut off power or reduce it below cavitation level before proceeding. It may
be necessary to use a centrifuge or high vacuum to reduce tenacious foam. If foam persists, the
sample may have to be discarded.
If foaming continues to be a problem, an indirect sonication
device (such as a Cup Horn) may be a better option.
Viscosity Limitations
Viscous solutions and highly concentrated liquids can be difficult to sonicate. If the liquid is so thick
that it will not pour or circulate easily it is too thick and cannot be processed effectively.
Keeping Samples Cool
Intense ultrasonic processing causes the liquid temperature to elevate especially with small
volumes. High temperatures reduce cavitation so the liquid should be kept as cold as possible. This
can be accomplished by immersing the sample vessel in an ice-salt-water-alcohol bath, or by using
a water-jacketed processing vessel with cold water circulation. To minimize temperature elevation,
use the pulse mode.
Free Radical Information
Trace free radicals produced by ultrasonics will usually have little or no enzyme activity. The free
radicals may be H
2
O
2
, O
3
as well as many other molecules and ions produced from air or water. If
this kind of reaction is suspected, it can easily be avoided by using CO
2
or N
2
atmosphere. A CO
2
atmosphere is quickly obtained by placing a pellet of dry ice in the solution before processing and
let it "bubble out". A CO
2
atmosphere stops luminescence in the cavitation bubble for the same
reason it prevents it in a vacuum tube. It is this luminescence which causes the water and air
molecules to break up producing the radicals. This CO
2
procedure, as simple as it is, again is
ordinarily unnecessary.