Centrifuge selection: matching the lab centrifuge and rotor to the protocol, choosing a centrifuge machine by force rather than by speed, and the containment and service questions that decide the real cost

Specifying from the protocol

1. Work in relative centrifugal force, not rpm. Protocols are written in relative centrifugal force because it is the physical quantity that separates material. The same rotational speed in two rotors of different radius gives very different force, so a machine specified on its top speed alone may not reach the force a method requires.
2. Fixed angle, swinging bucket or continuous. Fixed angle rotors pellet quickly and give a sloped pellet; swinging buckets give a flat pellet and suit gradients and plates; each has its own maximum force and its own tube set. Decide which protocols must run before choosing the machine, because the rotor range available is the real constraint.
3. Refrigeration and temperature control. Anything involving enzymes, live cells or long spins needs refrigeration, and a refrigerated unit costs considerably more to buy and to run. A lab that specifies ambient to save money and then needs cold spins ends up buying twice.
4. Containment where the sample is hazardous. Sealed buckets or a sealed rotor lid keep an aerosol inside the rotor if a tube fails, and they are what allows the rotor to be opened in a cabinet rather than at the bench. For infectious or human material this is a containment requirement, not an accessory.
5. Rotor life and service. Rotors are consumables on a long clock: they log cycles, they corrode, and manufacturers publish derating and retirement rules. Ask what the rotor log looks like, what the retirement policy is, and what a replacement costs, because that answer is frequently a large fraction of the machine price.

Benchtop, floor standing and microcentrifuge

A microcentrifuge handles small tubes at high force and is the workhorse of molecular labs. A benchtop unit takes plates, larger tubes and swinging buckets. A floor standing high speed or ultracentrifuge is a different class of purchase with its own siting, power and maintenance requirements, and is usually a shared resource rather than a group purchase.

Most labs need more than one, and the mistake is buying one machine that does everything badly rather than two that each do their job.

Siting, noise and imbalance

Centrifuges need a solid, level surface with clearance for ventilation, and they are loud. A high speed unit in a shared office-adjacent lab is a complaint waiting to happen, and moving it later is not trivial.

Imbalance detection is standard now, but it protects the machine rather than removing the need to balance properly. Train for it, because an unbalanced rotor at speed is the most dangerous routine failure in a normal lab.

Common questions

What is the difference between rpm and relative centrifugal force?

Rpm measures how fast the rotor turns; relative centrifugal force measures the force applied to the sample, and depends on both speed and rotor radius. Protocols specify force, so convert using the rotor's radius rather than matching rpm between machines.

Do I need a refrigerated centrifuge?

If you spin live cells, enzymes, nucleic acids or anything for an extended period, yes. Frictional heating during a long spin raises sample temperature noticeably even in a cool room.

When do I need sealed buckets?

Whenever a tube failure could release an infectious or toxic aerosol, including most work with human samples. Sealed carriers let the rotor be loaded and opened inside a biosafety cabinet.

How long does a rotor last?

Manufacturers set a life in cycles or years and publish derating for older rotors, and corrosion or a dropped rotor can retire one immediately. Keep a log, because the retirement rule depends on it.

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