Sunday, November 11, 2012

How to calibrate pipette ?

Calibrating pipette

Materials
Pipet – 10-20 pipet tips, Balance capable of accuracy and resolution to ± 0.1%, weighing vessel large enough to hold volume of liquid, Type I water, Thermometer and barometer.

Procedure

1.      Record the weight of the vessel. Record the temperature of water. Obtain the barometric pressure

2.      Place small volume 0.5 mL of water into the container. Avoid handling of container

3.      Weigh each container or set the balance to zero

4.      Using pipet draw the specified amount. Carefully wipe outside of the tip. Care should be taken not to touch the end of the tip.

5.      Dispense the water into the weighed vessel. Touch the tip to the side

6.      Record the weight of the vessel

7.      Subtract the weight obtained in step 3 from that obtained in step 6. Record the result.

8.      Repeat steps 1 to 6 minimum of nine times

9.      Obtain the mean of weight of water at given temperature. Multiply the mean weight by the corresponding density of water at given temperature and pressure.

10.  Determine the accuracy or the ability of the pipet to dispense the expected volume according to following formula

Mean volume/expected volume x 100%

The value should not differ more than 1.0% from the expected value.

Precision is calculated by calculating %CV or SD. required imprecision is usually ± 1SD or CV <0.1% for 1 ml.
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