Pippeting

Question 1

What are pipettes?

Answer 1

Pipettes are glass or plastic tubes, usually open at both ends, which are used to transfer specific amounts of liquid from one container to another

Question 2

What does to aspirate mean?

Answer 2

To draw up the liquid into the pipette tip

Question 3

What does to dispense mean?

Answer 3

To discharge the liquid from the tip

Question 4

What does to ‘blow out’ mean?

Answer 4

To discharge the residual liquid from the tip

Question 5

What are volumetric pipettes?

Answer 5

They are used to deliver a single specific volume of liquid, usually between 1 and 100ml

Question 6

Describe the appearance of a volumetric pipette.

Answer 6

They are shaped like rolling pins with a large belly, one blunt end, the neck,

Question 7

In terms of pipettes what does TD mean

Answer 7

To dispense

Question 8

In terms of pipettes what does TC mean

Answer 8

To contain

Question 9

What is the difference between MOHR and Serological Pipettes?

Answer 9

A MOHR pipette has graduations that end before the tip

Serological pipettes has gradation marks that continue to the tip

Question 10

What indicates that a pipette is a ‘blow out’ pipette?

Answer 10

If the serological pipette has a frosted band or two thin rings

Question 11

What is a pasteur pipette?

Answer 11

A plastic pipette that is roughly calibrated

Question 12

What are micropipettes?

Answer 12

Automatic pipettes used to accurately transfer small liquid volumes

Question 13

What are the two types of micropipetes?

Answer 13

Air displacement

Positive displacement pipettes

Question 14

Describe an air displacement pipette.

Answer 14

A certain volume of air remains between the piston and the liquid

Question 15

Describe a positive displacement pipette.

Answer 15

In positive displacement pipetting, the piston is in direct contact with the liquid

Question 16

What is an air displacement pipette used for?

Answer 16

They are meant for general use with aqueous solutions

Question 17

What are positive displacement pipette?

Answer 17

They are used for high viscosity and volatile liquids

Question 18

List the steps to operating the micropipette

11

Answer 18

Set the volume

Attach the disposable tip

Depress the plunger to the first stop

Immerse tip in sample

Draw up the sample

Pause

Start dispensing

Reach first stop

Expel - second stop

Withdraw the pipette

Release the plunger

Discard the tip

Question 19

What is forward pipetting used for?

Answer 19

Standard solutions including buffers, water, dilute saline and dilute acid and bases

Question 20

What is reverse pipetting?

Answer 20

High viscosity solutions (blood), small volumes, buffers with detergent and solutions that foam easily

Question 21

What is the difference between forward pipetting and reverse pipetting?

Answer 21

In forward pipetting the exact amount of solution to be dispensed is taken up into the pipette while in reverse pipetting more than what is to be dispensed is taken up into the pipette

Question 22

What is accuracy?

Answer 22

Accuracy means the closeness with which the dispensed volume approximates the volume set on the pipette

Question 23

What is precision?

Answer 23

Precision is the ‘scatter’ or reproducibility of individual measurements of the same volume

Question 24

List the factors that affect pippeting.

3

Answer 24

Temperature

Density

Altitude

Question 25

List the different types of contamination that can occur.

Answer 25

Pipette-to-sample

Sample-to-pipette

Sample-to-sample (carry over)

Question 26

What is pipette to sample contamination?

Answer 26

A contaminated pipette or contaminated tips can cause contamination of samples

Question 27

What is sample-to-pipette contamination?

Answer 27

Samples or aerosols from samples can enter the cone of the pipette

Question 28

What is sample-to-sample contamination?

Answer 28

The remains of sample A can mix with next sample B inside the tip and may cause a false test result