Chapter 6: Operation
Operating Considerations
6 - 6 100-413-016 Rev. C
6.2.3.1 Foaming or Aerosoling
Always place the horn deep enough below the surface of the liquid to ensure there
is no violent motion or agitation on the surface. This problem is more critical
when processing small volumes, for example, 0.3 to 5 ml, when a conical-shaped
tube or vial, such as a cut-down Eppendorf tube, is recommended. The conical
shape of this type of container effectively raises the liquid level without increasing
the volume, thereby permitting the horn to be inserted more deeply below the liq-
uid surface level.
If foaming occurs, it can be detected by a change in the sound level and a
fluctuating reading on the power meter.
Little or no energy couples reliably to the solution while aerosoling is oc-
curring, and excessive top-layer heating will result. Remedy this problem
by lowering the probe as deep as possible and placing the output power
control to position 1 or 2 for a few seconds. Then gradually advance the
power output control to the level required.
6.2.3.2 Discoloration of the Processed Sample
If the tip touches the side of a glass tube or beaker, small glass particles will be
released which gradually discolor the sample to a greyish color. Excessive tip cor-
rosion can also cause a greying or darkening condition.
6.2.4 Sterilizing and Preventing Cross-Contamination
Sterilize horns and tips by removing them from the converter and autoclaving
them. However, it is faster, easier, and equally effective, to sterilize horns by
immersion in a beaker of alcohol or other disinfectant and then turning the power
on for a few seconds. This technique also cleans or removes unwanted residue on
the horn or tip.
6.2.5 Disrupting Tissues and Solids
You can effectively homogenize or disrupt many kinds of tissue and other solids.
Energy radiates only from the horn’s tip. The energy is most concentrated within
1/2 inch (13 mm) of the face of the tip. When you treat tissue or solids already in
solution, the freely moving cells or particles pass before the face of the tip many
times during the process. When you treat a solid piece, however, the energy pat-
tern from the tip of the horn has a tendency to push or repel the solid away from
the tip. The solid does not receive treatment, but simply spins or circulates around
the container.
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