Laboratory Centrifuge: Centrifuges separate two substances of different densities by the application of centrifugal forces which may be several times that of gravity. Centrifuges used for the laboratory work are described in the following sections.
Horizontal Arm Laboratory Centrifuge
The construction of a simple manually driven laboratory centrifuge is shown in Figure 1.1. It consists of a rotating head carrying two or four free metal buckets. Glass centrifuge tubes are filled with the material to be separated and placed into the metal buckets. The head is driven manually using the crank. When the head starts rotating, the metal buckets start swinging outwards and finally reach the horizontal position at maximum working speed. During this process, the particles (which are normally denser than the liquid) sediment along the side (length) of the tube and finally reach the bottom of the tube. The contents of centrifuge tubes (either suspension or emulsion) undergo separation based on their densities. Once the crank is stopped, the rotating head along with buckets reaches the resting position. Then, centrifuge tubes are removed and decanted to collect supernatant liquid (low-density phase). The sediment mass (high-density phase) can then be collected.
This centrifuge is used for small volumes. This is also known as a low-speed centrifuge. The RCF obtained in small centrifuges is at 2000 g, at approximately 5000 revolutions per minute.
The construction of an angle centrifuge is shown in Figure 1.2. It consists of an electrically driven head carrying metal buckets. The unique feature of this centrifuge is that metal buckets (carrying centrifuge tubes) are held at 45 to 50° to the vertical axes, at resting as well as rotating positions. This centrifuge is operated at high speed so as to get an RCF of 10,000 g.
During centrifugation, the high-density particles have only a short path to travel to reach the sides of the tube. The particles present in the liquid should sediment rapidly and should not adhere to the sides of the tube.
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