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Technical work articles! Centrifugal force analysis of centrifuge

2018/12/17 11:06:42      click :
  The sedimentation of the centrifuge is directly linked to the centrifugal force, and the centrifugal force is linked to the centrifugation method and the rotation speed!
  The sequential application of the sedimentation field flow fractionation of the centrifuge can greatly extend the separation range of the molecular weight in one experiment. There are two ways to achieve sequencing: gradually changing the speed of the centrifuge or changing the density of the carrier. The concentration of sucrose is often increased in water. Start with a strong field to separate the sample with the smallest molecular weight, then gradually reduce the rotation speed or stop the rotation completely to promote the large molecular weight sample to leach out of the column. Using this sequence, the different sizes of polystyrene particles are successfully separated. Latex, which is equivalent to a 1000-fold difference in molecular weight.
  The rate zone centrifugation method is to load a density gradient medium (such as sucrose, glycerin, KBr, CsCl, etc.) into the centrifuge tube before centrifugation. The sample to be separated is placed on the top of the gradient liquid, at the bottom of the centrifuge tube or in the middle of the gradient layer. The gradient was centrifuged together. After centrifugation, the density of the medium at the near-rotation axis (X1) is the smallest, and the density of the medium (X2) farthest from the axis of rotation is the largest, but the maximum medium density must be smaller than the minimum density of particles in the sample, that is, ρP>ρm. According to the difference of sedimentation speed of the separated particles in the gradient liquid, the particles with different sedimentation speeds are divided into a series of zones in different density gradient layers to achieve separation from each other. The gradient liquid acts as a supporting medium and a stabilizer during the centrifugation and after centrifugation to avoid re-mixing of the layered particles due to mechanical vibration.
  Since ρP>ρm knows that S>0, the centrifugation time of the centrifugation method is strictly controlled, and there is sufficient time for the various particles to form a zone in the medium gradient, and to control before any particles reach the precipitation. If the centrifugation time is too long, all the samples can reach the bottom of the centrifuge tube; the centrifugation time is insufficient and the sample has not been separated. Since this method is an incomplete settlement, the settlement is greatly affected by the size of the substance itself, and is generally applied when the material size is different and the density is the same. Commonly used gradients are Ficoll, Percoll and sucrose.
  Conversion of centrifuge speed and centrifugal force: (calculation formula for centrifuge separation factor)
  1. The meaning of the separation factor:
  The ratio of the partition coefficients of the two solutes under the same conditions in the same extraction system. The larger (or smaller) the separation factor, the better the separation of the two solute, the separation factor is equal to 1, the two solutes are inseparable. The separation factor on the centrifuge refers to the relative centrifugal force.
  2. The main factors affecting the separation factor:
  Centrifugal force does not exist as a real force. In the non-inertial system, it is a force that is convenient for calculation. Please see the following instructions: Centripetal force causes an object to be attracted to a central point, or to repulsion or any tendency to point to it. Descartes interprets centrifugal force as a tendency for an object to maintain its "limited amount." The difference is that the centripetal force is under the inertial reference frame, and the centrifugal force is the force in the non-inertial system. When we deal with physics, we are all in the inertial system (Newton's law is established), so the concept of centrifugal force is generally not used. Since it is not a concept at all, we cannot compare their direction and size.
  F=mω2r
  ω: rotational angular velocity (radian / sec)
  r: distance of the rotating body from the rotating axis (cm)
  m: particle quality
  Relative centrifugal force (RCF)
  RCF is the multiple of the actual centrifugal force converted to gravitational acceleration.
  g is the acceleration of gravity (9.80665m/s2)
  The same rotation is equal to 2π radians for one week, so the angular velocity of the rotor is expressed in number of revolutions per minute (revolutions per minute n or r/min): In general, low-speed centrifugation is often expressed in terms of r/min.
  3. Calculation formula for separation factor:
  RCF=F centrifugal force/F gravity=mω?2r/mg= ω?2r/g= (2*π*r/r*rpm) ?2*r/g Note: rpm should be converted into rpm
  For example: a centrifuge with a diameter of 1000 mm and a speed of 1000 rpm, the separation factor is:
  RCF(1000)=(2*3.1415*16.667)^2*0.5/9.8
  =104.72^2*0.5/9.8
  =560
  The space is limited, today's information about the centrifugal force of the centrifuge is here, continue again next time!