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Transferring Centrifugation Parameters From a Protocol to Your Own Conditions

27.06.2018

What do you have to check and possibly adjust? We reveal the secret behind rcf and rpm and how to convert one to the other. Or you use our rcf/rpm online calculator.

If you follow a given protocol, make sure to use the same type of rotor and apply the given relative centrifugal force (rcf or g × force) as well as the same temperature and running time. In general, the following major parameters have to be determined to achieve a successful centrifugation run: 

  • A: Type of sample
  • B: Type of vessel
  • C: Type of centrifuge
  • D: Type of rotor
  • E: Necessary relative centrifugal force
  • F: Necessary temperature during centrifugation

Relative centrifugal force (rcf) influences running time and the quality of pellets and is determined by the type of sample, tube, rotor, speed, and centrifuge. When using rotors with different radii to spin a particular tube, please use the same rcf instead of the same revolutions per minute (rpm). To convert rpm and rcf you will need the maximum rotor radius and either the rpm value or the rcf value.

  • rpm = speed = revolutions per minute
  • rcf (... × g) = multiples of the Earth’s gravitational force = relative centrifugal force
  • rcm is the rotational radius measured in centimeters (cm) (distance from rotor axis to the bottom of the tube in cm)
  • nrpm is the rotating speed measured in revolutions per minute (rpm)

Because this issue is very important, many convenient conversion options now exist. The best, of course, is that the centrifuge itself provides an immediately accessible rpm/rcf conversion button directly on the centrifuge operating panel. This dispenses with having to carry out complex manual calculations.

Further options include calculating nomograms using the formula shown above. To convert rpm and rcf, you will need the maximum rotor radius and either the rpm value or the rcf value. Use a ruler to determine the necessary value. Such nomograms can often be found in operating manuals or on the internet pages of well-known centrifuge suppliers, too. Automatic calculators can be found there as well.

Rotational speed and centrifugal force

To calculate the relative centrifugal force at the given rotor speed and given rotor radius, please enter the values in the appropriate fields and press the "Calculate RCF" button.

The "Calculate speed" button provides information on the required rotational speed at the given relative centrifugal force and the given rotor radius.

Please enter the rotor's radius directly
= Radius      cm
Relative centrifugal force (RCF)

RCF      x g

 
Speed

Speed      rpm

The use of adapters influences rmax to a certain extent as well. The distance from the rotor axis to the bottom of the tube will be shortened, which leads to lower g × forces. To create accurate centrifugation conditions, you must subtract the bottom thickness of the adapter from rmax.

Options for calculating rpm or rcf

 

You will always need information about the maximum rotor radius rmax, rpm, or rcf to carry out a calculation.

  • Use the rpm/rcf conversion button found directly on a centrifuge.
  • Use the rpm/rcf conversion nomogram.
  • Find a calculator in the internet (homepages of centrifuge suppliers).
  • Use a smartphone app.
  • Manually calculate the rpm or rcf using the standard formula.
  • Consult the operating manual, which provides rotor and adapter specifications.
  • Note the following: When adapters are used, subtract their thickness from rmax or select this at the centrifuge menu or select the appropriate corrected g × force.

The optimal g-force for your sample strongly depends on the type of sample. In general, you can state the following for the g-force in decreasing order: virus particles, cell organelles > DNA > RNA > protein > cell culture, blood samples, environmental samples, urine, cell separation. We recommend checking these individually by referring to the scientific literature as there are no general or exact rules available. In general, when using special adapters, you need to decrease the selected radius setting as the tube with adapter is located nearer to the center of the rotor than without an adapter. If you do not reduce the radius setting, you would run your sample with a lower g-force than displayed.