When it comes to centrifuge rotors, there are lots of options to choose from, with the selection being potentially overwhelming at times. Thankfully, if you know what you’re looking for, the choice narrows significantly. There are really four main areas you need to look at:
- Compatibility with your centrifuge
- Compatibility with vessels
- Rotor style
- Maximum G-force
Let’s look at each of these in detail:
1. Compatibility With Your Centrifuge
If you’re shopping for a rotor for an existing centrifuge, then you’ll need to make sure the rotor is compatible with your existing unit. The accessories available on our site are organized by centrifuge model to ensure you don’t end up with something that doesn’t fit. Rotors are sometimes cross-compatible within the same product line, but are never cross-compatible across different manufacturers.
If you’re shopping for an entirely new centrifuge, when you’re selecting a unit, you should look at what rotors are available for each model and whether they are suitable for your application. For example, if you go with the Centrisart G-16 Benchtop Centrifuges, there are several compatible rotors to choose from.
Some of the rotor options for Centrisart G-16 Benchtop Centrifuges.
2. Compatibility With Vessels
Before shopping for a centrifuge rotor, you’ll likely have a good idea of the types of vessels you’ll be using. This will determine which rotors you can use.
Some of the rotor options for DM0636 Multi-Purpose Clinical Centrifuges.
If you’re planning on using microplates or PCR strips, you’ll need a special type of rotor to suit your respective need (more on that below).
You also need to consider how many vessels a rotor can hold. If you need high throughput, then you’ll likely need a large rotor (and centrifuge).
Keep in mind that small differences in tube size can be the difference between compatibility and non-compatibility for a particular combination of tube and rotor or adapter. A difference in tube diameter, length, or shape could mean you need a different configuration in order to spin them. Some manufacturers publish tables showing what kinds of tubes are meant for a particular rotor or adapter.
Tube and adapter compatibility table for the Frontier Rotor R-S4x250/4MI.
3. Rotor Style
You’ll often hear of two main styles of centrifuge rotor being discussed: fixed angle and swing out, but there are some specialized styles available too. We discuss each of these below.
Fixed Angle Rotors
Fixed-angle rotors hold tubes at a fixed angle. Vessels are held in a circular formation within the rotor, with the number of slots depending on the size of the unit and the vessels it accommodates.
The arrangement of tubes in a fixed-angle rotor means that it can often fit more tubes than a swing-out rotor of a similar size. This can make fixed-angle rotors more suitable for high-throughput applications.
During centrifugation, particles move outwards along the angle of centrifugal force. In a fixed-angle rotor, particles don’t have far to travel in that direction before they hit the wall of the tube. Upon impact with the wall, the particles slide down to the bottom of the tube, with the densest particles hitting the bottom first. In density gradient centrifugation applications, sedimentation is quicker than in a swing-out rotor, in which some of the densest particles may travel the full length of the tube before hitting the wall.
If you need to centrifuge at high speeds, fixed-angle rotors are usually more suitable. Their rigid design can withstand higher gravitational forces than swing-out rotors can. They are ideal for separating biological macromolecules, including DNA, RNA, and proteins.
With some fixed-angle rotors, you can opt for hermetic seals for biocontainment of hazardous materials.
Swing Out Rotors
Swing-out rotors have space for buckets (usually four) which hold your vessels. When the centrifuge starts, the bucket swings out to an angle that’s horizontal to the rotation axis. For a given swing-out rotor, you often have multiple options for buckets and inserts (also known as adapters). Inserts are placed in the buckets and have space for a particular type and size of vessel.
For example, there are lots of options with the Frontier FC5714 Multi-Pro Centrifuge. There are two different swing-out rotors available, each with a selection of compatible buckets and inserts.
Swing-out rotors are good for lower speeds and larger volumes. Common uses for swing-out rotors include separating large particles from solution and resolving samples in density gradients. In the latter case, where particles settle in layers with the densest particles at the bottom of the tube, with swing-out rotors, the layers maintain their orientation when the tube is at rest, so they remain relatively undisturbed.
As with fixed-angle rotors, with swing-out rotors, you sometimes have the option to purchase buckets with hermetic seals.
As the name suggests, tubes in a vertical rotor are in a vertical position. Vertical rotors are far less common than swing-out or fixed-angle and are used for specific use cases such as isopycnic separation and gradient density cushion separations.
Microplates need a special kind of rotor to hold them. Fixed-angle microplate rotors do exist but swing-out ones are more common.
PCR Strip Rotors
If you’re using PCR strips for your application, then you’ll need a rotor that accepts them. These come in various sizes, but often hold four strips of eight tubes. They are more commonly found for smaller centrifuges, such as mini centrifuges or microcentrifuges.
Some manufacturers produce combination rotors that can hold multiple different types of vessels, such as microtubes and PCR strips.
A COMBI-Rotor with Quick-Lock lid produced by Hermle which accepts microtubes and PCR strips.
4. Maximum G-Force
An important parameter to look at when shopping for a rotor is the maximum G-force, also referred to as the Relative Centrifugal Force (RCF). RCF is the force that’s being exerted on the rotor contents. While many scientific protocols reference RPM, you can only achieve reproducibility with RPM if you are using the same centrifuge and rotor.
It’s important to note the max RCF of both the centrifuge and the rotor. Most rotors can’t operate at a centrifuge’s maximum RCF, so the rotor max RCF will be the determining factor.
The Frontier Rotor R-A20x10 can handle a maximum RCF of 15,775 g.