Pippeting
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What are pipettes?
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
What does to aspirate mean?
To draw up the liquid into the pipette tip
What does to dispense mean?
To discharge the liquid from the tip
What does to ‘blow out’ mean?
To discharge the residual liquid from the tip
What are volumetric pipettes?
They are used to deliver a single specific volume of liquid, usually between 1 and 100ml
Describe the appearance of a volumetric pipette.
They are shaped like rolling pins with a large belly, one blunt end, the neck,
In terms of pipettes what does TD mean
To dispense
In terms of pipettes what does TC mean
To contain
What is the difference between MOHR and Serological Pipettes?
A MOHR pipette has graduations that end before the tip Serological pipettes has gradation marks that continue to the tip
What indicates that a pipette is a ‘blow out’ pipette?
If the serological pipette has a frosted band or two thin rings
What is a pasteur pipette?
A plastic pipette that is roughly calibrated
What are micropipettes?
Automatic pipettes used to accurately transfer small liquid volumes
What are the two types of micropipetes?
Air displacement Positive displacement pipettes
Describe an air displacement pipette.
A certain volume of air remains between the piston and the liquid
Describe a positive displacement pipette.
In positive displacement pipetting, the piston is in direct contact with the liquid
What is an air displacement pipette used for?
They are meant for general use with aqueous solutions
What are positive displacement pipette?
They are used for high viscosity and volatile liquids
List the steps to operating the micropipette 11
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
What is forward pipetting used for?
Standard solutions including buffers, water, dilute saline and dilute acid and bases
What is reverse pipetting?
High viscosity solutions (blood), small volumes, buffers with detergent and solutions that foam easily
What is the difference between forward pipetting and reverse pipetting?
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
What is accuracy?
Accuracy means the closeness with which the dispensed volume approximates the volume set on the pipette
What is precision?
Precision is the ‘scatter’ or reproducibility of individual measurements of the same volume
List the factors that affect pippeting. 3
Temperature Density Altitude