## Tips on Centrifugation without a Balance Tube

Safe centrifugation requires balanced loading of the centrifuge rotor. Imbalanced rotors can lead to damage to centrifuge rotors. When an odd number of tubes are loaded, a balance tube is loaded opposite the last sample tube. The balance tube must be identical to the sample tubes, and must contain liquid of equal density to the sample. Balancing by mass alone is not correct, since the centrifugal force that the sample applies to the rotor is dependent on both mass and radius.

See Figure 1 for balance loading patterns based on a 12-position microcentrifuge rotor.

### Table 1

Algorithms for Balanced

Requirements

• The rotor has n positions, such that n is divisible by 6, or
• If less than 6 an even number of positions.
• The number of samples is between 2 and n, but not equal to n-1.
• Tubes and sample volumes are identical.

Algorithm A. Sample number is even:

• Load pairs of tubes in opposite positions

Algorithm B. Sample number is odd:

• Load three tubes at equal intervals in the rotor, forming an equilateral triangle.
• Load the remaining tube in pairs in opposite positions.

Credits

Frothingham, R. (1999, February). Centrifugation without a balance tube. American Biotechnology Laboratory, 17, 84.

Dr. Richard Frothingham is a Staff Physician in the Infectious Disease Section, Durham VA Medical Center.
He is also an Assistant Professor of Medicine at Duke University Medical Center, Durham, NC.