To isolate components in a sample, protocols often include centrifugation. This can be performed with a wide variety of devices, some of which will be reviewed here. To keep a centrifuge working safely and effectively, it’s worth knowing something about them.
“The main purpose of a centrifuge is to separate material based on density, using centrifugal force, to allow separation of different components of your mixture,” says Michael Steinert, product marketing manager for biosciences at Cole-Parmer (Vernon Hills, IL). “The material separated can range from soil, yeast, cells, some proteins, and specific cell organelles.” He adds, “This allows you to remove the layers you are not studying from what you want to analyze.”
Like many instruments in a lab, the steps in operating a centrifuge depend on the device, but a few things apply to most platforms. Clinfield—a U.K.-based organization that trains nurses for work in clinical research—produced a how-to video on centrifugation. It notes a few key start-up steps to always follow, including manually spinning the rotor to make sure that it spins freely; the same should be done with swing-out buckets, if the centrifuge includes them.
In loading, balance is key. The tubes should weigh about the same and be placed evenly—such as on opposite sides when using only two tubes. When there’s a danger of spilling samples that could contaminate a centrifuge, lids should be added to the buckets, in addition to the lids on the individual tubes.
After that, the steps depend on the protocol and the centrifuge being used. In most protocols, the key is the g-force on the samples. If a centrifuge doesn’t allow a user to set the g-force, then it must be calculated, and the Clinfield video describes that process.
Centrifuge platforms cover various needs and spaces. For example, some can sit on a benchtop. Small benchtop centrifuges “can vary in capacity, speed, and application,” says Steinert. “For instance, small centrifuges—such as the Cole-Parmer Personal Microcentrifuge and the Cole-Parmer Variable Speed Centrifuge—are ideal for spin-downs of your liquid after mixing or vortexing to make sure that all the sample is at the bottom of the tube.” These usually spin at 1,500–9,000 revolutions per minute (rpm), and can be “used to separate or pellet materials that are easier to sediment, such as bacteria or small cell organelles,” Steinert says.
Some benchtop centrifuges provide more capacity, but don’t require much more space. For example, NuAire (Plymouth, MN) notes that its benchtop “NuWind Centrifuges offer larger capacity in a smaller footprint.”
Steinert points out that a larger benchtop centrifuge, like the Cole-Parmer MP315 Basic Centrifuge, “can be used for the same applications as their smaller counterparts but allow for separation of larger quantities more quickly. They also have an option to be refrigerated at varying levels, which makes it a good choice for samples that need to be kept at a certain temperature to remain stable.”
For faster spinning, scientists turn to ultracentrifuges, which crank up samples to 60,000 rpm or more. “These are used to separate smaller macromolecules, viruses, larger cell organelles, cell membranes, and are built for these applications,” Steinert explains. For example, NuAire’s himac CS150NX Tabletop Micro Ultracentrifuge can go up to 150,000 rpm. The company recommends this platform “when working with proteins, lipoproteins, cell organelles, DNA, RNA, viruses, carbon nanotubes, nanoparticles, and more.”
There are also specialty centrifuges for agricultural chemicals, food processing, water analysis, and other applications.
Keep it spinning
When asked about maintaining a centrifuge, Steinert says that it “should be cleaned with a neutral cleaning agent—a pH of 6 to 8—either daily or when polluted.” Do not use a caustic cleaning agent. Steinert continues, “After cleaning, each component should be rinsed with distilled water. Dry all the components with a soft cloth.” Everything needs to be dry to avoid any electrical issues. Plus, Steinert points out that “rotor pins should be kept clean and lubricated on a regular basis.”
On top of that, keep an eye on all of the parts. In every use, people in the lab should know how to look for wear and tear on a centrifuge. It’s really worth the trouble—if only to ensure that the rotor only spins inside the centrifuge, and nothing gets flung into a lab at high speed!
Mike May is a freelance writer and editor living in Texas. He can be reached at [email protected]