Centrifuge Basics

The first centrifuge was developed in 1878 and its purpose was to separate cream from milk. There’s been an almost exponential growth of centrifuge use and capabilities since. Today, the centrifuge is a common piece of lab equipment that’s used to separate particles according to their size, shape, density, and viscosity. They are found in a variety of industries, from food processing to molecular biology labs.

How Does a Centrifuge Work

All centrifuges use the sedimentation principle, which refers to the tendency of particles to settle and come to rest, or drift to the bottom. A centrifuge uses a motor to spin samples to accelerate sedimentation, causing a separation of particles. The speed the motor is spinning at is called the RCF, which is the relative centrifugal force.

In any solution, denser particles will sink, and lighter ones will float, the more centrifugal force applied to the top of the solution, the faster the separation. When the particles separate, gravity works to pull the heavier ones to the bottom of the container. There are different separating techniques that can be used, they are:

  • Pelleting technique
  • Isopycnic technique
  • Density gradient technique
  • Phase separation
  • Ultrafiltration technique

Different types of centrifuges are categorized by size, sample capacity, and rotor type. The rotor is a critical component in determining how the centrifuge can be used. It’s one of the many factors to consider when purchasing a centrifuge.

Factors to Consider When Buying a Centrifuge

Not all centrifuges work the same, have the same features, are used in the same environments and they definitely have different price points. There are several factors to consider when buying a centrifuge, a few of the key ones are listed below.

  • Speed regulation range: the speed capacity of the rotors is a critical part of the work that they’re needed for
  • Rotor imbalance: sensors that detect a rotor imbalance can save a lot of time and problems
  • Automatic setting resolutions: this allows you to set a centrifuge and it will automatically change settings without manually having to monitor the work
  • Display type: the display type is just a matter of ease of use and convenience, but it can be a determining factor
  • Dimensions and weight: when lab space is at a premium, the size of the centrifuge can be an important concern, similarly some centrifuges are very heavy, and others are portable
  • Floor standing or benchtop: this factor also plays into the space available and the size of the centrifuge
  • Function: probably the most important factor is what needs to be done and which centrifuge is the best option for that task

High-Speed vs. Low-Speed Centrifuge

A high-speed centrifuge is often required when high temperatures and great speeds are necessary for separation. This is the most common centrifuge and is what is typically used in a medical or biomedical facility. The speed of high-speed centrifuges can reach 16,000 rpm or more.

Contrasted with that, the low-speed centrifuge does not exceed a rate of 4000 rpm. You’ll find these slower centrifuges in some industries like textiles, chemicals, environmental protection, and some pharmaceutical companies.

Types of Centrifuge Rotors

Because the rotor is such an important part of the centrifuge, it’s important to understand some of the most common rotor types and to know which one is best suited for your application.

  • Swinging Bucket Rotors: This rotor starts with buckets that hang in a vertical position and swing out into a horizontal position during acceleration, looking quite like a carnival ride.
  • Fixed Angle Rotors: With this rotor the samples are held at a fixed angle, outward from the center. It’s the most common rotor found in a laboratory setting.
  • Continuous-Flow Rotors: This is considered a specialized rotor and isn’t used as often as the other two, but it can be very useful when separating large volumes at high speeds. Some situations where a continuous-flow rotor would be used is processing mitochondria, large viruses, bacteria, and tissue homogenates.
  • Drum Rotors: These are another type of specialized rotor that isn’t used as often as the swinging bucket or fixed angle rotors. They hold samples upright and can separate dense source material well, but drum rotors are not suitable for pelleting.

Where to Purchase Centrifuges

When purchasing a centrifuge, the primary consideration is what it will be used for and then the size and rotor speed are the next key pieces of information. After that, you need to know where to purchase your centrifuges. Here, at the New York Microscope Company, we have a large variety of centrifuges for purchase and our skilled staff can help you select just the right piece of equipment for your needs.