Centrifuges are essential pieces of laboratory equipment utilized for separating particles from a solution based on their size, shape, density, and viscosity. The effectiveness of this separation process is contingent on the rotor speed. Nowadays, laboratory centrifuges are among the most widely used tools in both research and clinical settings. They are prevalent in various types of laboratories, with a particularly high usage rate in chemistry, biochemistry, and molecular biology labs.
These versatile instruments find application in tasks such as the separation, purification, and isolation of organelles, cells, and cellular components. Additionally, they are invaluable for dealing with complex mixtures of nucleic acids, proteins, and viruses, facilitating further detailed analysis.
Centrifuges have a rich history, initially employed for separating cream from milk since the late 1800s. However, their capabilities, specifically the maximum centrifugal force they could generate, didn't experience significant advancement until progress in biochemistry spurred a demand for devices with higher levels of centrifugal force. This need, first in the separation of cell components, and later in the escalating demand for virus research, catalyzed numerous developments in centrifugation technology. These advancements collectively culminated in what we now recognize as the modern commercial centrifuge.
In this post, we'll cover what a centrifuge does and how it works, as well as what types of centrifuges and rotors are commonly used in lab research. We'll also review the average cost and compare buying a new or used centrifuge vs. leasing.
Centrifuges separate heterogeneous mixtures into their various components – liquids in liquids, solids in liquids, and liquids in gases, based on the different densities of the components. One of the most common uses is to separate red blood cells and other blood components from whole blood.
A centrifuge works based on the sedimentation principle. Sedimentation refers to the tendency for particles in suspension to settle out of the medium where they are entrapped and come to rest against a barrier. The centrifuge uses centrifugal acceleration to separate the particles out of the solution.
If the solution has a higher density than the solvent, the particles will sink to the bottom of the tube. If the solution has a lower density than the solvent, the particles float to the top.
The greater the difference in density between the solution and the solvent, the faster the particles move. If the density between the two remains the same, the particles remain steady in the solution.
In situations where particles need to be separated from a solution where there is little to no difference in density, the centrifuge creates a centrifugal force to separate the particles, instead of relying on gravity to do the work.
A centrifuge uses a motor to spin liquid samples at high speed. The speed at which a centrifuge’s rotor moves is often expressed as RCF, short for relative centrifugal force, in units of gravity (x g).
However, many devices will display the speed in RPM, or revolutions per minute. Centrifugal force moves the dense components to the outside of the container allowing the solids to settle completely and rapidly.
There are different types of centrifuges, which vary in size, sample capacity, and rotor type. The rotor type plays a key role in your decision-making when it comes time to acquire a centrifuge for your laboratory. That’s because the rotor effects which types of applications you can perform.
Furthermore, centrifuges utilize glass or plastic tubes that fit in the rotor cavities. The size and type of the sample tubes influence the samples that can be used in the unit.
For example, glass tubes can be used with the majority of solvents but are often more expensive. Plastic tubes, when used with care, can be just as durable, however, water is the preferred solvent. If you need to work with larger samples, you’ll want to use centrifuge bottles instead of tubes.
Also known as benchtop centrifuges, these collect small amounts of material such as yeast cells and erythrocytes. Small bench centrifuges have a maximum relative centrifugal field of 3,000 to 7,000x the force of gravity, known as gravitational force or g-force (g).
Compared to other options, these are relatively low speed. These are a general-purpose centrifuge and are among the most affordable options available today.
Large capacity refrigerated centrifuges feature a refrigerated rotor chamber. It’s possible to change rotor chambers to accommodate another size. They collect substances that sediment rapidly, similar to like small bench models, and with a maximum speed of 6,500 g.
High-speed centrifuges are much like the large capacity models, except they can reach max speeds of about 60,000 g. These models can collect larger cellular organelles, cellular debris, microorganisms, and proteins precipitated by ammonium sulfate. The refrigerated models can also feature a refrigerated rotor chamber.
Ultra centrifuges are optimized to spin at very high speeds, capable of reaching as high as 1,000,000 g (9,800 kilometers per second or 6,089 miles per second). These kinds of centrifuges are classified as either preparative or analytical.
Preparative ultracentrifuges reach about 600,000 g. They are used to determine the shape and mass of macromolecules, separate lipoprotein molecules from plasma, and a variety of other tasks. Preparative ultracentrifuges feature chambers that are refrigerated, sealed, and evacuated.
With an analytical ultracentrifuge, there are three optical systems to choose from: 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, whereas a light absorption system detects changes via ultraviolet light absorption. These models run at about 500,000 g.
Beyond the type of centrifuge itself, it’s also important to consider the centrifuge rotor, as the rotor design influences what the machine can do and how much it costs.
These rotors feature buckets that start in a vertical position and swing into a horizontal position during acceleration. The tube and its solution are aligned parallel to the centrifugal field and perpendicular to the axis of rotation.
With this rotor design, the sample types are held at a constant fixed angle – one that falls anywhere between 14 and 40. The relative centrifugal force means the particles have to move outward and collide with the outer wall of the centrifuge tube.
A region of higher concentration is formed, and this area has a greater density than the surrounding medium. The precipitate collects as a compact pellet at the outermost point of the tube.
There aren’t nearly as many applications that require specialized rotors like continuous-flow rotors or drum rotors compared to fixed angle or swinging bucket rotors. But, when it is needed, you see how important continuous flow really is.
It is considered a time-saver, making efficient work of separating large volumes of materials at high centrifugal forces without the repetitiveness of filling and decanting dozens of centrifuge test tubes or frequently starting and stopping the rotor.
Flow rotors are best suited for applications such as processing cell and algae harvest, mitochondria, large viruses, bacteria, and tissue homogenates.
Centrifuge costs exhibit a wide range, contingent upon factors like size, type, and included features. Here are average price ranges by type:
It's important to note that incorporating refrigeration into any of these centrifuges will elevate the overall cost. Additionally, opting for customization and the potential purchase of extra rotors can further increase expenses.
Furthermore, it's worth considering that the specific needs of a laboratory may impact the choice of centrifuge. Factors like sample volume, required centrifugal force, and the types of samples being processed will play a crucial role in determining the most suitable centrifuge for a given application. It's recommended to consult with a specialist or supplier who can provide tailored advice based on the unique requirements of the laboratory.
Depending on the type and number of units you need, acquiring a centrifuge can involve a significant upfront capital investment. The price can vary depending on other factors like additional features or customizations essential for your lab's operations. Benchtop centrifuges are less expensive than other types of laboratory centrifuges, and can be easy to procure. However, for more expensive purchases, purchasing may not always be the most feasible option for labs operating on a budget.
Opting to lease a centrifuge through Excedr offers a practical alternative. This approach allows you to obtain the necessary equipment without incurring a hefty initial cost. In addition to the cost savings compared to an outright purchase, leasing eliminates the hassle of managing annual service contracts, as maintenance and repairs are typically included in the lease agreement. Furthermore, leasing provides the flexibility to upgrade your equipment at the conclusion of the lease term.
Leasing a centrifuge can be a strategic move, especially for labs seeking to optimize their financial resources while ensuring access to state-of-the-art equipment. If you're interested in exploring our leasing program further, don't hesitate to contact us today for more information on the benefits and process.