A centrifuge is a piece of equipment that separates particles from a solution, according to the size, shape, viscosity, and density of the medium, a process that is dependent on the speed of the rotor.
Particles in a solution that has a higher density than the solvent sink and are known as sediment. Particles that are lighter float to the top. The greater the difference in density, the faster the particles move. If there is no difference, the particles stay steady in the solution.
If you need to separate the particles from a solution where there is little difference in density, rather than using gravity, you can use centrifugal force, which is provided by the centrifuge. Why is this important in biotechnology? It separates the cell organelles and assists in complex experiments that require separating subcellular parts.
Types of Centrifuges & Their Uses
Small Bench Centrifuges
This type of centrifuge is used to collect small amounts of material that rapidly settle to sediment, such as erythrocytes, yeast cells, etc. A small bench centrifuge has a maximum relative centrifugal field of 3,000 to 7,000 x gravity (g).
Large Capacity Refrigerated Centrifuges
These centrifuges have a refrigerated rotor chamber. They also have the option to change rotor chambers for another size. Their maximum speed is 6,500 g. They are used to collect substances that rapidly sediment, such as chloroplasts, nuclei, and erythrocytes.
High-Speed Refrigerated Centrifuges
This kind of centrifuge reaches speeds of about 60,000 g. As such, it is used to collect proteins precipitated by ammonium sulfate, cellular debris, micro-organisms, and larger cellular organelles.
This type of ultracentrifuge produces a relative centrifugal force of about 600,000 g. The chamber is refrigerated, sealed, and evacuated. An ultracentrifuge can determine the shape and mass of macromolecules, separate lipoprotein fractions from plasma, assist in ligand binding kinetic studies, and more.
This type of ultracentrifuge can operate at 500,000 g. Analytical ultracentrifuges are available with three kinds of optical systems. These include a light absorption system, the Schlieren system, and the Rayleigh interferometric system. The Schlieren and Rayleigh systems are used to detect changes in the refractive index of the solution.
Types of Centrifuge Rotors
There are different types of rotors for centrifuges, which influence what the centrifuge does and how much it costs.
Also referred to as swinging bucket rotors, these rotors have buckets that start in a vertical position. During acceleration, the buckets swing to a horizontal position so that during centrifugation the tube and the solution in the tube are aligned perpendicular to the axis of rotation and parallel to the centrifugal field. The tube returns to its original position as the rotor decelerates.
Generally, swing bucket rotors support two separation types —rate-zonal and isopycnic. For rate-zonal separations, swing buckets are preferred because the distance between the outside of the meniscus and the outside of the bottom of the tube is long enough for adequate separation to occur.
Fixed angle rotors hold tubes at a constant fixed angle, generally anywhere between 14° and 40° to the vertical. The centrifugal field forces particles to move radially outward and have only a short distance to travel before they collide with the outer wall of the centrifuge tube. As a result, a region of high concentration is formed that has a greater density than the surrounding medium. The precipitate sinks and collects as a small compact pellet at the outermost point of the tube.
Because of this, they are often used for pellet applications to either pellet particles from a suspension and remove the extra debris or to collect. When deciding to use a fixed angle rotor, consider the K factor. The K Factor indicates how efficient the rotor can pellet at maximum speed. The lower the K-factor, the higher the pelleting efficiency.
Vertical Tube Rotors
These rotors are considered zero-angle fixed-angle rotors where the tubes are aligned vertically in the body of the rotors all the time. These are highly specialized pieces of equipment that are generally used to band DNA in cesium chloride. These rotors have low K factors, which is useful if the particle only needs to move a short distance until it pellets.
Elutriator rotors are a type of continuous flow rotator that feature recesses to hold a cone-shaped separation chamber. The point of the cone points away from the axis of rotation. It is counterbalanced by a bypass chamber on the opposite side of the rotor, which also provides the fluid outlet.
Zonal rotors can either be a continuous flow type or a batch type. The batch type is more widely used than the continuous flow option. The batch rotor is designed to minimize the wall effect encountered in a swinging bucket and fixed-angle rotors and to increase the sample size.
Handle all rotors with care to prevent scratching. Wash with deionized water and dry thoroughly to prevent corrosion. Store in a clean and dry environment. Do not submerge swing-bucket rotors in water because they are difficult to dry.
Average Centrifuge Cost
Centrifuge equipment pricing varies depending on the brand, make and model, and the type. Top manufacturers include Thermo Fisher, Eppendorf, Sigma, and Ohaus. Price ranges for each type are:
- Benchtop – $1,000 to $5,000
- Large Capacity / High Speed – $10,000 to $25,000
- Ultracentrifuge – $10,000 to $50,000
It’s possible to get refrigeration on all these types of centrifuges. Those units tend to fall into the higher end of the spectrum. You can also customize and buy additional rotors, but doing so adds to the final cost.
Leasing vs. Buying Centrifuge Equipment
When it comes to buying a centrifuge, you could end up investing a rather large amount of your working capital upfront, depending on the type, the number of units, add-ons, and customizations your lab needs. Though centrifuges are not as expensive as other types of equipment, when you’re on a budget, purchasing them may not be practical.
While there’s always the option to buy a refurbished unit, you’re still left with the cost of maintenance and repair outside of any warranty coverage that may be included. The warranties often provide limited, short-term coverage that isn’t useful in the long-term.
Leasing your laboratory equipment, on the other hand, allows you to make the most of your budget. There’s a significantly reduced upfront cost required, and repairs and maintenance are covered for the life of your lease. Your lease will cost a fraction of the price it costs to purchase the equipment outright while giving you the freedom and flexibility to upgrade your lab equipment at the end of your lease term.
In some cases, you’ll be able to save even more money because your lease payments will be tax-deductible, though you’ll need to speak with an accountant as rules and regulations vary depending on your location and industry. Contact Excedr today to learn more about a centrifuge lease.