This set of Bioseparation Processes Multiple Choice Questions & Answers (MCQs) focuses on “Laboratory Centrifuge”.

1. Which centrifuge is used for small-scale separation?

a) Laboratory centrifuge

b) Preparative centrifuge

c) Ultracentrifuge

d) Disk bowl centrifuge

View Answer

Explanation: The laboratory centrifuge is used for small scale separation and clarification of particles from liquid and it can handle liquid volumes of 1-5000ml range. The material to be centrifuged is appropriately distributed in centrifuge tubes and then they are attached in a symmetric manner to the rotor.

2. What are the types of rotor?

a) Unfixed angle rotor, swing in rotor

b) Swing out rotor, swing in rotor

c) Fixed angle rotor, unfixed angle

d) Fixed angle, swing out rotor

View Answer

Explanation: The two types of rotor are fixed angle rotor and swing out rotor. A fixed angle rotor can hold the centrifuge in a fixed position at a particular angle to the axis of rotation and the swing out rotor can hold the tubes parallel to the axis of rotation.

3. What is the range of rotation speed of laboratory centrifuge?

a) 500-1000rpm

b) 1000-15000rpm

c) 1000-1500rpm

d) 5000-15000rpm

View Answer

Explanation: The rotation speed of laboratory centrifuge ranges from 1000 to 15000 rpm and the magnitude of the induced gravitational field is measured in the terms of gravitational pull i.e. G value.

4. What is G value?

a) RPM

b) Gravity

c) RCF

d) Anti-gravity

View Answer

Explanation: G value refers to the relative centrifugal force and the value of 1000 refers to an induced field that is thousand times stronger than the value obtained due to gravity. It depends on the rotation speed and the angle at which the centrifuge tubes are oriented.

5. What is the equation for G value?

a) G = \(\frac{r\omega^2}{g}\)

b) G = –\(\frac{r\omega^2}{g}\)

c) G = \(\frac{\omega^2}{g}\)

d) G = \(\frac{r-\omega^2}{g}\)

View Answer

Explanation: G = \(\frac{r\omega^2}{g}\) is the equation for G value where, r is the distance from the axis of rotation, ω

^{2}is the angular velocity, g is the acceleration due to gravity and n is the rotation speed of the centrifuge.

6. Which parameter is important for the G value in the centrifuge?

a) Temperature

b) Pressure

c) pH

d) location

View Answer

Explanation: G value in a centrifuge is dependent on the location of the tube. The highest G value is observed at the bottom of the tube and the lowest G value is observed at top of the tube. It shows that a particle experiences an increase in G value while moving towards the bottom of the centrifuge tube.

7. What is the range of G value in laboratory centrifuge?

a) 500-1000

b) 1000-20000

c) 1000-1500

d) 1000-15000

View Answer

Explanation: The G value for laboratory centrifuge is 1000 to 20,000. The nomograms provided by the manufacturers of the centrifuge correlate the radial distance as well as rotation speed with the G value and it is commonly used in the calculations based on laboratory scale centrifuge.

8. What is the empirical correlation used for estimation of centrifugation time?

a) t = –\(\frac{k}{S}\)

b) t = \(\frac{-k}{S}\)

c) t = \(\frac{k}{S}\)

d) t = \(\frac{k}{-S}\)

View Answer

Explanation: The particles settle by going through different zones of G value while moving towards the bottom of the centrifuge tube and the empirical correlation is commonly used for the estimation of complete centrifugation time is t = \(\frac{k}{S}\) where, k is the k factor of the centrifuge, S is the Svedberg coefficient of the material being precipitated and t is the complete sedimentation time.

9. How to obtain k-factor using empirical correlation?

a) k = 2.53 × 10^{11}\((\frac{ln\,(r_{max} – r_{min})}{rpm_{max}^2})\)

b) k = 2.53 × 10^{11}\((\frac{r_{max} – r_{min}}{rpm_{max}^2})\)

c) k = 2.53 × 10^{5}\((\frac{ln\,(r_{max} – r_{min})}{rpm_{max}^2})\)

d) k = -2.53 × 10^{11}\((\frac{ln\,(r_{max} – r_{min})}{rpm_{max}^2})\)

View Answer

Explanation: The k-factor can be obtained by using equation, k = 2.53 × 10

^{11}\((\frac{ln\,(r_{max} – r_{min})}{rpm_{max}^2})\) where, r

_{max}is the radial distance from the axis of the bottom of the tube, r

_{min}is the radial distance from the axis to the top of the tube, rpm

_{max}is the maximum rotation speed. A small k factor results in a faster centrifugation process.

10. Which rotor will take less time for precipitating the sample?

a) Both fixed angle and swing out rotor

b) Both unfixed angle and swing in rotor

c) Fixed angle rotor

d) Swing out rotor

View Answer

Explanation: Fixed angle rotor requires less time for precipitating the sample and the distance travelled by the particle for precipitation is less. The fixed angle rotor are heavier and require much heavier energy to operate while the swing out rotor are used for centrifuging substances with high sedimentation coefficient such as cells and coarse particles.

11. Estimate the G value for a centrifuge when distance of tubes from axis of rotation is 1.5m, angular velocity of the rotating tubes is 2.5 rad/s and the rotation speed is 2.5/s.

a) 6.01

b) 5.01

c) 4.01

d) 3.01

View Answer

Explanation: G = \(\frac{r\omega^2}{g} = \frac{2\pi rn^2}{g}\) so, G = \(\frac{2\pi × 1.5 × 2.5^2}{9.8} \) = 6.01 ∴ G = 6.01.

12. Calculate the complete sedimentation time required for the centrifugation to take place when radial distance from the axis to the bottom of the tube is 2.5cm, radial distance from the axis to the top of the tube is 0.5 cm, the maximum rotation speed is 20000/min and the Svedberg coefficient of the material being precipitated is 1.2.

a) 500min

b) 400min

c) 365.35min

d) 350 min

View Answer

Explanation: t = \(\frac{k}{S}\) where, = 2.53 × 10

^{11}\((\frac{ln\,(r_{max} – r_{min})}{rpm_{max}^2}\)) so, k = 2.53 × 10

^{11}\((\frac{ln\,(2.5 – 0.5)}{20000^2}\)) = 438.42 ∴ t = \(\frac{4.38.42}{1.2}\) = 365.35min.

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