Contemporary modifications of filtration and dialysis use a matrix-based fibrous material that provides a mechanism of separation in many homogeneous immunoassays.
These materials may be coated with specific antibody-ligand to foster selection of specific materials or species.
Certain labels use magnetic particles in conjunction with strong magnets to effect separation. Basic universally used separation mechanisms, outside of those incorporated in immunoassay, are centrifugation, filtration, and dialysis.
Centrifugation is a process in which centrifugal force is used to separate solid matter from a liquid suspension.
The centrifuge carries out this action. It consists of a head or rotor, carriers, or shields that are attached to the vertical shaft of a motor and enclosed in a metal covering. The centrifuge always has a lid and an on/off switch; however, many models include a brake or a builtin tachometer, which indicates speed, and some centrifuges are refrigerated. Centrifugal force depends on three variables: mass, speed, and radius. The speed is expressed in revolutions per minute (rpm), and the centrifugal force generated is expressed in terms of relative centrifugal force (RCF) or gravities (g). The speed of the centrifuge is related to the RCF by the following equation:
RCF 1.118 105 r (rpm)2 where 1.118 105 is a constant, determined from the angular velocity, and r is the radius in centimeters, measured from the center of the centrifuge axis to the bottom of the test-tube shield. The RCF value also may be obtained from a nomogram similar to that found in
Appendix F on the book’s companion website. Centrifuge classification is based on several criteria, including benchtop or floor model, refrigeration, rotor head, or maximum speed attainable (i.e., ultracentrifuge).
Centrifuges are generally used to separate serum or plasma from the blood cells as the blood samples are