Centrifugal force and principle of rotor centrifuge tube

When the Centrifuge rotor rotates at a certain angular velocity w (radians/second) and the radius of rotation of the particles is r (cm), any particles are subjected to an outward centrifugal force. The centrifugal force is: F = mω2r 1

Where F is usually expressed in gravity, called relative centrifugal force (RCF),

The relative centrifugal force means that in the centrifugal force field, the centrifugal force acting on the particles is equivalent to a multiple of the earth's gravity, and the unit is the gravitational acceleration g (980 cm/sec 2). At this time, the RCF can be expressed as follows: RCF = ω2r/980 2

In fact, this relationship is commonly used in revolutions per minute n (r/min or rpm), expressed in more general expressions, since ω = 2πn/60 then:

RCF=4Ï€2 ( rpm) 2r/3600*980 3

Simplified:

RCF=1.119×10-5 ( rpm) 2r 4

Generally, the rpm is usually used for low speed, and the high speed is expressed by g.

(a) centrifuge tube

Common glass centrifuge tubes are hard but brittle and cannot withstand the pressure of ultracentrifugation.

The centrifuge tubes used in the rotor of the ultracentrifuge are classified into two types: plastic tubes and stainless steel tubes.

When centrifuging, the sample should generally be filled with a centrifuge tube. Otherwise, the outside of the tube may be unevenly pressed due to air bubbles, causing the tube to rupture and causing an imbalance in the rotor.

(2) Centrifugal cap

The centrifuge tube used in the ultracentrifuge is usually equipped with a cap, and the cap is required to be worn when the centrifuge is centrifuged.

(3) Rotor and selection

There are several types of angular rotors (Type), horizontal rotors (sw), vertical rotors (v), and zoned rotors (c).

1. Angle rotor

Refers to the rotor with a certain inclination angle of the centrifuge tube and the rotating shaft. The larger the angle, the stronger the settlement and the better the separation effect. On the contrary, the smaller the angle, the shorter the sedimentation distance of the particles and the faster the sedimentation speed, but the separation effect is poor. When the particles settle in the angular rotor, they first collide with the centrifugal tube in the direction of centrifugal force, and then slide along the tube wall to the bottom of the tube. Therefore, particle deposition occurs on one side of the tube, which is called “wall effect”. Zui is suitable for differential centrifugation, which is strong and convenient, but it stirs the sample when accelerating or decelerating.

2, horizontal rotor

The centrifugal tube in the movable sleeve of the rotor is rotated from the vertical suspension to the horizontal position (about 200-800 rpm) as the rotor rotates. The sedimentation of the particles in the horizontal rotor is in the direction of the tube. In the gradient centrifugation, the particle sedimentation zone traverses the centrifuge tube. After centrifugation, the zone does not have to be repositioned, but only the particles in the center of the sample zone are directly settled to the bottom of the tube. The particles hit the sides of the wall, creating a "wall effect," but the convection was much less affected by vibration and shifting.

3, vertical rotor

The special form of the angle rotor is mainly used for equal density gradient centrifugation. This rotor particle has a short moving distance and saves a lot of time compared with the horizontal and angle rotors, but the speed is easily changed to cause convection disturbance.

4, zone rotor