Centrifuges are among a select group of laboratory instruments that are as scalable as they are configurable. Individuals who have used benchtop centrifuges that handle sub-milliliter volumes may be surprised to learn that centrifuges— some as large as rooms—are used in industrial processing.
Basic centrifuge designs are simple, consisting of an enclosed compartment inside which a rotor spins rapidly. Rotors, which can usually be interchanged, contain equally spaced openings into which sample tubes are inserted. Samples will either spin at a fixed angle relative to the rotating axis or “swing out” to perpendicular under centripetal force as the rotor speed increases. Forces generated as the rotor spins cause components in the sample to migrate toward the bottom of the sample tube, according to weight or density.
Entry-level mini-centrifuges easily fit on a benchtop, operate at a single, relatively low speed, generate low gravitational (g) forces, and cost only a few hundred dollars. “Minis” are used for samples whose components are easily separated by density. Most medical and veterinary office centrifuges are of this type. The next level up, compact benchtop centrifuges, spin tubes of up to about 2 mL and create tens of thousands of g’s. Researchers use them to separate DNA, proteins, and cellular components.
There are many ways to differentiate centrifuges by type, speed, and features. Beckman Coulter (Fullerton, Calif.), for example, divides its product line into three basic platforms: benchtop devices operating at up to about 10,000 rpm, “washing machine” centrifuges that provide up to about 100,000 g, and ultracentrifuges that deliver in excess of one million g. In fact, one could argue that all centrifuges exist along a continuum of features that may be mixed and matched, which include g-force generated, sample tube size, refrigeration capabilities, rotation angle, computerization, and others.
Michael Rosenblum, marketing VP at LabNet International (Edison, NJ), offers the following considerations when purchasing a lab centrifuge:
- What size tubes do you expect to run?
- How fast does your sample need to spin to achieve the desired separation?
- Is an angled rotor or a swing-out rotor best for your application?
- Does your sample require refrigeration?
- What is the range of applications you are likely to encounter?
Angled vs. swing-out tube design affects speed and g-force, and provides sample collection options (spin-out is slower but provides a clean pellet). Refrigeration is desirable because samples heat up during a long run. It all comes down to your expected application range and the likelihood that the instrument you buy will be flexible enough to meet your needs.
Price was conspicuously absent from the list because lab centrifuges tend to be inexpensive compared with other high-use lab instruments. The price “sweet spot” of about $300 for unrefrigerated, single-speed mini-centrifuges up to about $6,000 for high-speed, refrigerated benchtop instruments covers most applications in the life sciences and other industries.
• Spins tubes from 0.2 ml to 50 ml as well as microplates
• Features a maximum speed of 17,500 rpm
• Small footprint – requires only 15 inches of bench space
• A refrigerated model is also available
Eppendorf North America
•Provides fast separations for samples as small as 175 µl up to 13.5 ml
• Features speeds up to 150,000 rpm and RCF of more than 1,000,000 x g
• Includes a customizable touch-screen user interface for up to 12 individuals
• Includes software that enables users to spec- ify up to five steps, set multiple programs or delay start time
• Includes a multi-memory function that allows recall of up to 6 sets of operating conditions
• Features a power-saving mode, which activates after a period of standby
• Set temperature of 4°C from ambient temperature of 25°C is reached in about 5 minutes
• When temperature inside chamber increases in power saving mode, the system will automatically cool the chamber
ROTINA 380 R
• Features a maximum speed of 15,000 rpm
• Features infinitely variable refrigeration from -20°C to 40°C
• Maximum capacity in swing-out rotor: 4 x 290 ml
•Maximum capacity in an angle rotor: 6 x 94 ml