Omni International: Rotor Stator Generator Probes

Rotor Stator Generator Probes

Q: How do rotor stator generator probes work?
A: The rotor shaft is coupled directly to the drive motor and spins at up to 35,000 rpm (depending on product choice). The rotating knife and shaft makes up the rotor portion of the rotor stator generator probe. The tube and collar assembly attaches to the motor housing, but does not spin, and is therefore called the stator. As the knife spins within the stator, it creates a pumping action which pulls liquid into the open end of the generator probe, and forces the liquid out through windows on the stator portion of the generator probe. The interaction of the knife with these windows sets up a shearing action, much like a pair of scissors, and thereby works to reduce the particle size of sample being forced through the windows. The speed differential between the rapidly moving liquid being pumped by the rotating knife, and the relatively stationary liquid which makes up the rest of the sample, sets up a second force, called cavitation. This force literally acts to pull the sample apart, and therefore further reduces particle size. Constant circulation continues to re-subject the sample to these forces, and therefore further reduces particle size as a function of processing time. A practical limit of minimum particle size is generally determined by the material itself, the processing time, and the spacing between the rotor knife and the stator’s tube and collar.

Q. What diameter generator probe should I use?
A: Choose a diameter size according to the volume of sample being processed when working with liquids, or according to the inside diameter of your vessel when working with solids. Optimal operating efficiency is generally achieved when the vessel diameter is approximately ten times the diameter of the generator probe. For solids, try to choose a generator probe whose diameter is as large or larger then the initial particle size of the sample being processed.

Q. Should I choose a saw tooth or flat bottom generator probe?
A: Saw tooth generator probes perform better with tissue samples and other fibrous material. Flat bottom generators are useful for gentler applications, such as creating emulsions, basic mixing, or liquid-liquid processing.

Q. What length should I choose for my generator probe?
A: Your generator probe should be long enough to almost reach the bottom of your processing vessel while keeping the upper aeration hole above your sample level. Processing efficiency is affected by the distance of your generator probe from your vessel’s bottom, the vessels size and geometry as well as by the sample itself. It may be beneficial to experiment with a variety of distances between the generator probe and vessel bottom. A location of 1/3 of the distance from the bottom to the liquid level is a good starting point.

Q. Are Omni International generator probes easy to clean?
A: Yes, they are easy to disassemble and clean. Complete instructions are included with all generator probes.

Q. Should I be concerned about material leaching?
A: For some applications, such as soil analysis for instance, some of our customers have expressed concern about elemental leaching from the generator probe to the sample. In many cases, titanium generator probes can solve this problem. Please call Omni at 1-800-776-4431 for details.

Q. Should I worry about sample to sample contamination?
A: In some applications, such as DNA or RNA extraction for PCR, elimination of sample to sample cross contamination can be critical. Our Stainless Steel generator probes are easy to clean. In other cases, it may be important to keep the sample safely sealed and isolated from the environment. For this application, sealed chamber assemblies are recommended. Call Omni International for complete details.

Q. Do I need to be concerned about aerosols?
A: If you are processing potentially hazardous or pathogenic material, we strongly urge you not use an open container, since the homogenization process will create aerosols. For this application, sealed chamber assemblies are recommended. Call your representative or Omni for complete details.

Q. Will my samples foam during processing?
A: Some foaming is always possible, but our generator probes are specifically designed to reduce foaming.

Q. What is the difference between rotor-stator and ultrasonic homogenization?
A: Rotor-stator generator probes disrupt samples by means of mechanical shearing. Ultrasonic homogenizers disrupt samples by means of high-intensity ultrasonic waves, which create microscopic bubbles referred to as “cavitation.” Ultrasonic homogenizers are ideal for cellular disruption, e coli, yeast, fungi, and bacteria processing. Rotor-stator generator probes are more effective at processing soft or hard tissue samples. Rotor-stator technology also emits much less heat and noise when compared to ultrasonic homogenizers. Both types of technologies can minimize or eliminate cross contamination and sample carryover.

Q. What if my sample is very granular, or extremely fibrous?
A: Open blades can be an ideal method for pre-processing the sample, prior to processing with a generator probe. In many cases, the open blade alone is capable of performing the entire processing task.

Q. How can I reduce the swirling that sometimes occurs when using a generator probe?
A: The processing vessel’s shape can have major impact on the flow characteristics of the sample. A fluted vessel, or a vessel with corners, can disrupt swirling flow patterns and significantly increase processing efficiency.

Q. At what speed, or what setting should I operate my homogenizer for maximum efficiency?
A: The smaller generator probes, 10mm and below in diameter, can be operated at full speed, although many applications may call for gentler or slower processing. Larger generator probes, 20mm and above should not be operated above their “optimal speed range”. Exceeding the recommended maximum speed will actually decrease the efficiency of the system. For the Omni Mixer or Omni Macro, a motor speed indicator is recommended to determine exact motor speed.

Q. How can I find out more about processing my specific application?
A: Omni International has thousands of customers around the world, many of whom share their problems and successes with our applications staff. Please call us at 1-800-776-4431, and we will do our best to help you succeed with your specific need.

Q: Can the stainless steel probes be autoclaved?
A: As long as the stainless steel probe is supplied with a Teflon upper bearing, the entire assembly may be autoclaved. If the probe is supplied with a stainless steel ball upper bearing, you must first remove the ball bearing prior to autoclaving.

Q: Does the 5mm and 7mm probes (including the Omni Tips) fit into a 1.5mL and/or 2mL microcentrifuge tube?
A: Yes. Both the 5mm and 7mm probes will homogenize directly in a 1.5mL or 2mL microcentrifuge tube. The 2mL sample tube is usually preferred by most customers since the tube is round bottom rather than conical. This allows the probe to reach the bottom of the sample tube, therefore assuring complete homogenization.