Physiological skills 2
pre-prac prep
Practical Convenors:
Atarah Rass &
Kamano Mochoele
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PIPETTES
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Image created using biorender
Plastic Pasteur pipettes
Different means of measuring
and transferring liquids in the
lab
Graduated, used for non-quantitative non-precise transfer
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https://www.hiclipart.com/free-transparent-background-png-clipart-hpcnm/download
Serological pipettes
Different means of measuring
and transferring liquids in the
lab
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Used for quantitative transfers
Needs a vacuum source to aspirate (pipettor or bulb)
Graduated in 1/10th of a mL up to 50 mL
https://www.carlroth.com/at/en/single-use-pasteur-pipettes/serological-pipettes-rotilabo/p/n232.1
Micropipettes
Different means of measuring
and transferring liquids in the
lab
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Single channel used for highly accurate volume transfers
Ranges from 0.1 µL to 10 mL
https://theminione.com/product/one-series-micropipette-set-ea1010/
Volume adjustor
Parts of a
micropipette
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Volumeter display
Pipette etiquette
These pipettes are not toys. They are top of the line, expensive equipment and we demand that
you use them responsibly. Here are a few rules:
1.
Always use a disposable tip and never draw any fluid into the white barrel (tip holder) of the pipette
itself. The P-20 and P-200 use the yellow tips (sometimes clear) and the P-1000 use blue tips
(sometimes clear).
2.
Never lay a pipette down while there is fluid in the tip. The fluid may accidentally find its way into the
barrel.
3.
Never turn the volume adjuster below or above the full range settings.
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How to set your pipette
to the correct volume
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200-1000 uL pipette (Blue tips)
First RED number is the thousands place of µL:
0350 µL
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20-200 uL pipette (Yellow tips)
First number is the hundreds place of µL: 095 µL
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2-20 uL pipette (Yellow tips)
First number is the tens place of µL; RED number
is after the decimal: 02.5 µL
How to correctly
place your tip
1.
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Open tip box
2.
Firmly place pipette
into tip and twist 90o
before removing.
3.
Close tip box
Forward pipetting
Step by step directions:
1.
Set the desired volume.
• Turn the volume up just a tiny bit past the desired setting, then down.
2.
Attach a tip.
• Press it on firmly, with a slight twisting motion. The tip must make an airtight seal with the pipette barrel. Do not tap or bang pipette into tip!
*Hold pipette upright while pipetting - accuracy*
3.
Depress the plunger to first stop.
• Most people operate the plunger with their thumb
4.
Insert the tip in the liquid you want to transfer.
• Not far, just a bit below the surface; pre-wet tip by aspirating up and down
twice.
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https://www.microlit.us/faqs/what-are-the-different-techniques-of-pipetting/
5.
Release plunger s l o w l y .
• Releasing the plunger suddenly may cause the pipette to
underfill.
• Also, be aware that the liquid level in the tube will drop as
you withdraw fluid. Make sure that it doesn't drop below
the level of the tip or you will suck air.
6.
As you withdraw the tip, touch it to the side wall of the
tube to remove excess fluid from the exterior.
7.
To dispense, depress plunger slowly to the first stop;
hesitate; then depress all the way.
• Never dispense a small volume into thin air. Always
dispense into a liquid or onto the wall of a tube so that
adhesion will draw the expelled liquid off the tip.
8.
Think about what to do with the pipette tip. Should you discard
it or use it again?
•
"If in doubt, throw it out."
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(Pushparaj, 2019)
Important actions
Effect of pipetting position on accuracy
Correct droplet dispensing position
INCORRECT
Droplet hangs on
tip rather than
dispensing into
tube
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CORRECT
Droplet adheres
to the wall of the
tube
CORRECT
Droplet dispersed
directly into liquid
in the tube
Accuracy & Precision
Percent Error = [(actualpredicted)/predicted] * 100%
The purpose of calculating the percent error
is to analyse how close the measured
value is to an actual value.
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