A review of centrifuge fundamentals, with focus on advanced features and capabilities of new technologies
Few instruments are as essential as laboratory centrifuges. Ranges of size, speed, and capacity make them versatile for a wide array of applications such as microfuge sample prep, ultrahigh-speed separations, cell culture isolation, and many others. Each device type is accompanied by considerations of ease-of-use, safety, maintenance, and more.
Modern centrifuge technologies have sought to address these aspects, while incorporating advanced features to extend instrument capabilities. Instrument vendors have created resources, training, and tips to enhance the user experience as well.
What is centrifugation?
Centrifugation is a technique which involves the application of centrifugal force to separate particles from solution, based on size, density, viscosity, and other properties.
When only the force of gravity is applied, the size and density of a particle correlates with the rate that particle separates from solution. The larger and denser the particle, the faster it separates from solution.
How does a centrifuge work?
Application of a larger effective gravitational force, such as centrifugal force provided by a centrifuge instrument, results in an accelerated rate of particle separation.
- The rate of centrifugation is specified by angular velocity, expressed in revolutions per minute (rpm).
- Particle separation can be expressed as RCF or relative centrifugal force (force x gravity; g-force; or g).
- The conversion factor between RPM and g depends on the radius of the centrifuge rotor, as RPM is simply the speed of the rotor and g is the force applied to the contents within the rotor.
- This conversion is: RCF = 1.1118 x 10-5 x r x rpm2; where r is the radius of the rotor in centimeters.
- The instrument housing contains the centrifuge motor, electronics, gears, ventilation or refrigeration components, and other functional essentials.
- The drum forms a barrier between the rotor and the housing, preventing damage due to sample spinning and spillage.
- The rotor contains chambers for sample vessels, which may include microtubes, falcon tubes, bottles, or in the case of ultracentrifuges, polycarbonate or polypropylene screw tube spin tubes or bottles.
- The rotor can be open, sealable through the use of a screw top lid or may include interchangeable inserts, such as swinging buckets, plate holders, and other accessories.
- The rotor is placed and secured onto a spindle, which is directly connected to the instrument motor – which together form the mechanical basis of rotation.
- The lid may include a latch or lock, depending on intended use and model type.
The motor and spindle can typically receive the most wear, and can be directly impacted by the rotor and samples therein. An essential practice is the careful balancing of samples within the rotor in order to minimize adverse effects on these components and the instruments in general.
Types of centrifuges
Bench Top centrifuges have been traditionally tasked with low-mid speed isolation of cells or cellular materials, biochemical reagents, and particulates in suspensions (although benchtop high/ultrahigh-speed analytical instruments are also common). Fixed angle or swinging bucket exchangeable rotors have made these centrifuge types versatile for a large number of cell biological and clinical applications.
More recently, benchtop instruments have excelled in their efficient use of space and smaller footprints – lab space having now become an evermore precious commodity. These centrifuges can range in capacity from 1 to 3 Liters or more, and can routinely accommodate swing out rotors, round buckets with 5/10/15/50 mL inserts, and plate holders -- for applications including sample processing, cell harvesting, pelleting, and separating blood, cells, and other biological materials.
Floor versions of the above general-purpose instruments provide similar performance without sacrificing bench space – ideal when dedicated space or an equipment room is preferred. These versions can add enhanced stability for vibration and refrigeration control as well.
High-speed Centrifuge and Ultracentrifugation
These centrifuges are reserved for high and ultra-high speeds, with acceleration reaching over 100,000 x g. The capabilities of both analytical and preparative device models extend the range and scale of separations – ideal for method development and transition to standardized protocols.
Microcentrifuges or microfuges are truly lab essentials – used for isolating small-scale cellular material or quickly spinning sample preparations. These are classified as accommodating samples in microfuge tube volumes, typically less than 2.0 mL. Speeds can range from <10,000 x g to 16,000 x g or more depending on type and model.
New centrifuge features and technologies
- New technologies often include easy alignment and locking methods which allow facile changing of rotors, without tools or difficult procedures.
- New digital control features allow users to access advanced functions via a keypad or touchscreen. Some control centers are plug and play, permitting use of the interface with multiple devices.
- On-board data systems allow users to access multiple preset or programmable methods, enabling fast operation and enhancing between-run precision.
- These data systems can also relay service reminders, keep a log book of accessories, record instrument operator ID and usage, and more.
- Diagnostic features, such as end of run notification alerts and rotor imbalance alarms, add to the ease-of-use and safety aspects of the devices.
- Beyond these, modern instruments may include rotor recognition technology which limits the speed of specified rotors. Imbalance protection can stop the rotor if imbalance thresholds are exceeded. Power factor controls can enhance uniformity of voltage and amperage, thereby increasing run to run precision.
Refrigerated versus Ventilated Centrifuge
- Many modern centrifuges are offered in both refrigerated and non-refrigerated or vented models, depending on needs. Ventilated models are designed to maximize air flow from external sources, through the instrument housing, motor assembly, and drum – thereby limiting excessive heat from extended runs. The faster the motor runs the higher the air flow rate.
- Refrigerated units make use of advanced refrigerants (such as CFC-free or green solutions), increasing cooling efficiency while decreasing energy consumption. Precision temperature control systems ensure maximum performance and sample protection.
- Instrument vendors have invested considerable efforts in ensuring instruments are operated correctly and efficiently. Recognizing an instrument as a lab essential includes realizing that the devices often see many different operators with a range of experience levels. Training programs and online resources are intended to infuse quality control and standard operating procedures to centrifuge usage.
Safety and Maintenance Resources
- In addition to on-board diagnostics and safety features, online resources are also available to minimize safety issues and clarify maintenance questions -- all to enhance the user experience and extend the life of the devices.
Modern centrifuge technologies bring smart capabilities to these essential lab instruments. Advanced control features, on-board methods and diagnostics, enhanced safety measures and resources, enable modern devices to run circles around traditional centrifuge instruments.
Where can I find centrifuge instruments, rotors, parts, and accessories?
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