Glossary of Terms

ACCELERATION TIME
ACCELERATION TIME of a rotor to its maximum speed varies with the rotor, the centrifuge, and the acceleration program selected by the user.

AVERAGE RADIUS
AVERAGE RADIUS of a rotor is the distance from the center of rotation to the midpoint of the centrifuge tube during centrifugation.

CENTRIFUGAL FORCE
CENTRIFUGAL FORCE (symbol: g) is exerted on a rotating body or particle, tending to pull it away from the center of rotation.

CLEARING
CLEARING is the removal, by sedimentation in a centrifugal field, of particles from a supernatant.

CLEARING FACTOR
CLEARING FACTOR (symbol: K) is a constant, different for each rotor, used to compare the relative efficiency of rotors for pelleting operations:

K = tS,

where t is the clearing time of a specified particle in hours and S is the sedimentation coefficient of that particle in Svedbergs

CLEARING TIME
CLEARING TIME is the time required to sediment a particle in aqueous solution to the bottom of a centrifuge tube:

t = K/S,

where t is the clearing time in hours, K is the clearing factor for a specific rotor, and S is the sedimentation coefficient of the particle in Svedbergs

Acceleration and Deceleration times are not taken into effect when total run time is calculated. Run times may be longer for most metallic rotors although their clearing factor may appear to have better sedimenting efficiency than comparable carbon rotors. Carbon Fiber rotors are lighter and accelerate and decelerate faster than metallic rotors...

DECELERATION TIME
DECELERATION TIME of a rotor from its maximum speed varies with the rotor, the centrifuge, and the deceleration program selected by the user.

DENSITY
DENSITY is the mass per unit volume of a substance, often expressed in g/ml.

DENSITY GRADIENT CENTRIFUGATION
DENSITY GRADIENT CENTRIFUGATION is separation performed in a supporting column of solution in which the density and solution concentration increase toward the bottom of the centrifuge tube.

DERATION
DERATION of rotors, after a specified amount of use, guards against the effects of metal fatigue.

DIFFERENTIAL CENTRIFUGATION
DIFFERENTIAL CENTRIFUGATION separates particles on the basis of their size. By a series of centrifugations at various speeds and times, different-sized particles are sedimented and collected from an initially homogenous suspension.

DISCONTINUOUS, OR STEP, GRADIENT
DISCONTINUOUS, OR STEP, GRADIENT is one composed of layers, with abrupt changes in density and/or concentration from one layer to the next.

ELC
ELC is Enhanced Liquid Containment. Some models of High/Super Speed rotors have a special lid and curve annulus at the top of the rotor. The annulus is designed to contain a volume of liquid equal to one bottle/tube that leaks from the bottle/tube during cetrifugation, thus eliminating rotor imbalance if the fluid is leaked and escapes from the rotor.

EQUILIBRIUM, OR ISOPYCNIC, GRADIENT CENTRIFUGATION
EQUILIBRIUM, OR ISOPYCNIC, GRADIENT CENTRIFUGATION separates particles on the basis of their buoyant densities. A gradient range is selected to encompass the densities of all particles to be banded. Equilibrium gradients may be self-generated by centrifugal force acting on a solution of uniform starting density, or they may be preformed by layering to achieve equilibrium more rapidly.

GRADIENT LAYERING
GRADIENT LAYERING is the process of making a preformed discontinuous gradient by means of a mechanical pump or a Pasteur pipette.

IMBALANCE (rotor imbalance)
Carbon fiber rotors are not susceptible to slight imbalances as do metallic rotors, because of their light weight. Carbon fiber rotors also do not elongate at high speeds as do metallic rotors, therefore imbalances of approximately 1% of sample volume per tube in small rotors, and 2.5% to 5% of sample volume per tube in large volume rotors can be tolerated in carbon fiber rotors. The metallic rotors are restricted to imbalance tolerance of 0.5% for small rotors and 2% for large volume rotors. In carbon fiber rotors tubes can be filled at equal levels "by eye" whereas with metallic rotors tubes must be filled and balanced within 0.1 to 2.0 grams per tube according to rotor volumes.

ISOPYCNIC GRADIENT CENTRIFUGATION
ISOPYCNIC GRADIENT CENTRIFUGATION. See EQUILIBRIUM GRADIENT CENTRIFUGATION.

K-FACTOR.
K-FACTOR. See CLEARING FACTOR

MAXIMUM RADIUS
MAXIMUM RADIUS (symbol: rmax) of a rotor is the distance from the center of rotation to the bottom of the centrifuge tube during centrifugation.

MINIMUM RADIUS
MINIMUM RADIUS of a rotor is the distance from the center of rotation to the inside (centripetal) top edge of the centrifuge tube during centrifugation

MOLECULAR WEIGHT
MOLECULAR WEIGHT (symbol: M) is the sum of the atomic weights of all the atoms in a molecule.

NOMINAL TUBE VOLUME
NOMINAL TUBE VOLUME is that which a centrifuge tube would hold if completely filled. The actual fill volume under operating conditions, however, will be somewhat less.

OVERSPEED DISK
OVERSPEED DISK is s ring with alternating light and dark sector-shaped stripes that is attached to the bottom of each preparative ultracentrifuge rotor. An essential part of the photoelectric overspeed detection system, it should be replaced if damaged or when the rotor is derated.

PELLETING
PELLETING is the process of sedimenting material to the bottom of a centrifuge tube.

PELLICLE
PELLICLE is a film or floating layer at the top of a centrifuge tube, following centrifugation.

RADIUS
RADIUS (symbol: r) of a rotor is the distance from the center of rotation.

RCF
RCF is the symbol for RELATIVE CENTRIFUGAL FIELD.

REFRACTIVE INDEX
REFRACTIVE INDEX (symbol: n) is the ratio of the velocity of light (at a particular wavelength) in a vacuum to that in a medium, such as water.

RELATIVE CENTRIFUGAL FIELD
RELATIVE CENTRIFUGAL FIELD (symbol: RCF) is the ratio of a centrifugal field, at a specific speed and a specific radius, to the earth's field of gravity:

RCF = 1.12 r (RPM/1000)^2

where r is the radius in millimeters and RPM is the speed of rotation in revolutions per minute (rpm)

REORIENTATION
REORIENTATION of the solution within a centrifuge tube changes its position in all fixed angle, vertical tube, and near vertical tube rotors. During centrifugation, the solution orients perpendicular to the axis of the rotor; it reorients to its original position after centrifigation.

ROTOR CAPACITY
ROTOR CAPACITY is the maximum volume of liquid (both sample and gradient) that a rotor can carry with all tubes full

SELF-GENERATING GRADIENT
SELF-GENERATING is one that is generated during centrifugation by resistribution and sedimentation of an initially uniform concentration of the gradient medium and sample solution.

SHORT COLUMN METHOD
SHORT COLUMN METHOD is the practice of partially filling centrifuge tubes in order ro reduce the sedimentation pathlength, thereby reducing the run time.

SHORT GRADIENT
SHORT GRADIENT is one with a rapid rate of change in density along the gradient column

STEP, OR DISCONTINUOIS, GRADIENT
STEP, OR DISCONTINUOIS, GRADIENT is one composed of layers, with abrupt changes in density and/or concentration from one layer to the next.

SUPERNATANT
SUPERNATANT is the liquid in a centrifuge tube above a pellet or sediment, after centrifugation.

SVEDBERG

SVEDBERG (SYmbol: S) is the unit used to express the sedimentation coefficient, where

S = 1 x 10^(-13) seconds

TUBE SIZE
TUBE SIZE is the length of a centrifuge tube, often given in both inches and millimeters.

TUBE VOLUME
TUBE VOLUME see NORMAL TUBE VOLUME.

WEIGHT/VOLUME (Symbol: w/v)
WEIGHT/VOLUME (Symbol: w/v) is the percent concentration of a solute in a solution, by weight per unit volume. For example, 20% w/v = 20 g of solute in 100ml of solution.

WEIGHT/WEIGHT (Symbol: w/w)
WEIGHT/WEIGHT (Symbol: w/w) is the percent concentration of a solute in a solution, by weight. For example, 20% w/w = 20 g of solute in 80 g of solution. This concentration is used in density gradient centrifugation.