Centrifuge: rotor types

The centrifuge is a laboratory equipment that generates rotational movements, it has the objective of separating the components that constitute a substance. Today there is a diversity of centrifuges that have different objectives, regardless of the type of research or industry. Depending on the type of centrifuge, each one will have different operation and characteristics (type of rotor and type of sample holder tube).

The two main types of rotors used in laboratory centrifuges are horizontal (also called tilting bucket) and fixed angle (or angled head).

What is the difference between these types of centrifuge rotors?

Horizontal rotors are so named because the buckets or racks that support the centrifuge tubes are suspended in a way that allows them to tilt upward in the horizontal plane when under the influence of a centrifugal field. Therefore, when operating the centrifuge, the particles settle along an unobstructed radial path, away from the center of rotation, and settle uniformly to the bottom of the tube or other container. The flat upper surface of the settled material simplifies the extraction of the supernatant from a loose granulate. Using multiple adapters, more than one tube type or size can be centrifuged, provided the load is properly balanced

Fixed angle rotors hold tubes at an angle to the axis of rotation. The angle varies with different rotors, being common between 25 ° and 40 °. Although the particles settle along a radial path on these rotors as well, they soon hit the opposite side of the tube where they slide down the wall to the bottom. The result is faster settling than can be achieved in horizontal rotors that have a longer settling path. But because the bottom of the tube is not aligned with the direction of the centrifugal force, the particles will partly accumulate along the side of the tube.

What applications do each have?

Within these two categories of rotors, various models offer different combinations of capacity and maximum achievable RCF. Horizontal rotors, in particular, have accessories that adapt them to a wide range of applications. The buckets suspended from the rotor fork can carry large containers such as blood bags or vials. Adapters are available for these buckets so that a number of small tubes can be operated simultaneously for applications such as RIA. The horizontal rotors can also be fitted with racks or holders, instead of buckets, which are suitable for centrifuging RIA tubes or micro test plates.

When rapid precipitation of small particles is required, fixed angle rotors should be used. Due to their design, these rotors are capable of higher speeds than the horizontal type. Sedimentation of larger particles, such as cells, protein precipitates, antigen adsorbing complexes, urinary crystals, can be done at lower speeds with horizontal rotors. With the latter, the maximum centrifugal force can be obtained if a wind-shielded version is used. Cell density separation is best done in a horizontal rotor of any type.

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