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Centrifugation

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Words 416
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Introduction:
Centrifugation is a process used to separate or concentrate materials suspended in a liquid medium. The theoretical basis of this technique is the effect of gravity on particles in suspension. Two particles of different masses will settle in a tube at different rates in response to gravity. The centrifugal force generated is proportional to the rotation rate of the rotor and the distance between the rotor centre and the centrifuge tube. There are three general classes of centrifugation which is low speed, up to about 5000rpm, high speed machines of up to about 25000rpm and ultracentrifuges which will turn at up to 100000rpm. Another form of centrifuge in laboratories is microcentrifuge. It is very common and simple machine used with 0.5 or 1.5ml disposable plastic tubes. Most of these machines generate between 10000 and 13000rpm. Many microcentrifuges only have settings for speed (rpm), not relative centrifugal force (rcf). Consequently, a formula for conversion is required to ensure that the appropriate setting is used in an experiment. The relationship between rpm and rcf is as follow, g=1.118 x 10ˆ-5 rs² where g is the relative centrifugal force, r is the radius of the rotor in centimeters and s is the speed of centrifuge in rpm.

Objective: 1. To determine the relationship of speed of centrifugation with the coagulation of milk which separate from the mixture. 2. To separate coagulated milk from the mixture of fresh milk and acetic acid by centrifugation.

Materials:
Centrifuge, 15ml centrifuge tubes, 1.5ml microcentrifuge tubes, micropipettes, fresh milk,
50% of acetic acid, Falcon tube

Procedure: 1. 5ml of fresh milk is drawn by the pipette into centrifuge tube which contains 50% of 10ml acetic acid. 2. Centrifuge tube was inverted gently for a few times to mix both solutions. 3. Milk sample was centrifuged at 1300rpm for 10 minutes and the coagulated milk solid was pelleted. 4. 1ml of milk was transferred to the centrifuge tube. The centrifuge tube was centrifuged at 5000rpm for 15 minutes. 5. 1ml of milk was transferred to the microcentrifuge tube and it was centrifuged at 13000rpm for 15 minutes. 6. The differences between these tubes were observed at the end of the procedure.

Result: Centrifugation | Centrifuge tube | First centrifugation | An oily, white curd coagulate on the Centrifuge tube wall. It gave a cheese smell. | Second centrifugation | The supernatant is transparent. The pallet became condensed. | Third centrifugation | A thin layer of white foam is formed on top of the supernatant. |

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