What Is A Centrifuge & What Does It Do in a Lab?

a centrifuge spinning samples and a diagram showing how it works inside the centrifuge

Last updated on April 18, 2023 by Ben

Centrifuges are common pieces of lab equipment, used to separate particles from a solution. These particles are separated according to the size, shape, density, and viscosity of the medium. The separation process depends on the rotor speed. 

Laboratory centrifuges are one of the most common pieces of lab equipment today. They are used in both research and clinical settings and can be found in numerous laboratories, but are perhaps most often used in chemistry, biochemistry, and molecular biology labs. 

Some of their most common applications include separation, purification, and isolation of organelles, cells, and cell components, as well as more complex mixtures of nucleic acids, proteins, and viruses for further observation.

Although centrifuges have a long history—they were first used to separate cream from milk since the late 1800s, their capabilities (maximum centrifugal force) didn’t see much advancement until progress in biochemistry led to a subsequent demand for devices with higher levels of centrifugal force. 

These demands—the need to separate cell components, and later, an increased demand in virus research—led to several development in centrifugation technology, ultimately leading to what we now know as the commercial centrifuge.  

What Does A Centrifuge Do?

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.

How Does a Centrifuge 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.

Types & Uses of Centrifuges

Small Bench Centrifuges

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

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 Refrigerated Centrifuges

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

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

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.

Analytical Ultracentrifuges

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.

Types of Centrifuge Rotors

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. 

Swinging Bucket Rotors

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.

Fixed Angle Rotors

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. 

Continuous-Flow Rotors

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.

How Much Does a Centrifuge Cost? 

Centrifuge costs vary widely depending on the size, type, and features of the unit. Average prices by type are:

  • Benchtop – $1,000 to $5,000
  • Large Capacity / High Speed – $10,000 to $25,000
  • Ultracentrifuge – $10,000 to $50,000

Adding refrigeration to any of the centrifuges will cause the price to be higher. Customization along with the option to purchase additional rotors also increases the cost.

Leasing vs. Buying A Centrifuge

Buying a centrifuge means investing a considerable amount of capital upfront, depending on the number of units you need, the type of centrifuge, and the add-ons and customizations your lab needs. 

Though centrifuges are not as costly as other types of lab equipment, purchasing may not be the most practical option for labs on a budget.

Leasing centrifuges through Excedr makes it easy to get the equipment your lab needs without making that hefty upfront investment. 

Not only will you save money compared to the initial purchase, but you’ll save yourself the headache of dealing with annual service contracts, because maintenance and repairs are included in the lease. Plus, you’ll have the option to upgrade your equipment at the end of your lease term.

Contact us today to learn more about leasing centrifuges.