Techniques For Optimizing Results - Qsonica SONICATOR S-4000 Operation Manual

9. 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 ¾" below the liquid surface.
Immersion depth can be less for larger horns and may have to be more for smaller probes
used at higher intensity.
Foaming and Aerosoling
Aerosoling and foaming generally occur when the tip is not immersed far enough into the
solution. Lowering the tip in the solution, decreasing power, and reducing solution
temperature will normally 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:
Use a narrower processing vessel
Use a vessel with an irregular inner surface
Increase effective viscosity by concentration or by adding glass beads.
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 or Microplate 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 or if 25-micron glass powder will not settle to
the bottom quickly, 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 a 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
or water. If this kind of reaction is suspected, it can easily be avoided by using CO
atmosphere. A CO atmosphere is quickly obtained by placing a pellet of dry ice in the
2
solution before processing and let it "bubble out". A CO
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 procedure, as simple as it is, again is ordinarily unnecessary.
2
O , O as well as many other molecules and ions produced from air
2 2 3
atmosphere stops luminescence in
2
30
or N
2 2