Mechanical homogenisers are used for a range of tasks in the lab, from preparing biological samples for DNA analysis and PCR work, to creating emulsions or mixing liquids.
This wide range of application means that a wide range of different probes are available to attach to the main motor. These vary greatly in size, material and capability – so how can you choose a suitable probe?
We’ve taken a look at the main points you need to consider when selecting a probe, to make sure you get the right tool for the job.
What is a rotor stator generator probe?
This refers to the construction of the probe, made up of a rotating knife portion and a stationary stator cover.
The rotor shaft couples to the motor and spins according to the motor settings. This rotating knife makes up the rotor part.
The outer tube and collar attach to the motor housing, but do not move during homogenisation, and so are referred to as “stator”.
As the rotor moves within the stator, a pumping action is set up which pulls liquid into the open end of the generator probe and forces liquid out through the stator windows. The shearing between the knife and the windows reduces the particle size.
The difference in speed between the fast moving liquid being drawn into the probe, and the stationary liquid elsewhere in the vessel set up another force called cavitation. This pulls the sample apart, further reducing the sample size.
These two forces together work to reduce particle size over time. The final particle size is determined by the sample itself, the processing time, and the space between the rotor and stator portions of the probe.
What diameter probe should I use?
If you’re working with solids, choose the probe diameter based on the vessel diameter to ensure it fits, but also try to choose a probe whose diameter is as large or larger than the initial particle size of the sample to be processed.
What length of probe should I use?
The probe should almost reach the bottom of the processing vessel while still keeping the upper aeration hole above the sample level.
Efficiency is afected by the distance of the probe from the bottom of the vessel, the vessel size and shape as well as the sample type.
You may need to experiment with different probe sizes to find the optimal one, but as a general rule of thumb set the probe to sit 2/3 in the sample, 1/3 away from the bottom of the vessel.
Saw tooth or flat bottom probe?
For tissue samples or fibrous materials, select a saw tooth probe.
In gentler work like creating emulsions, basic mixing or liquid-liquid processing, a flat bottom probe should be chosen.
How can I reduce cross contamination of samples?
The stainless steel probes by Omni can be taken apart for thorough cleaning – instructions on how to do this are supplied with the probes.
For additional protection against cross-contamination, you could consider using disposable probes – these allow a new probe to be used in each sample, eliminating cross contamination.