PRACTICAL 3

Digestive enzymes, specificity and pH: Appendix: Use of automatic pipettes

Use of automatic pipettes

You will make extensive use of automatic pipettes with disposable tips in these practicals. Please treat these with care. Do not drop them. There are three different pipettes which are used for different volume ranges. Make sure you select the correct pipette and tip (yellow tips for orange and yellow button pipettes; blue tips for blue button pipettes)

 

Volume range (µl)

Volume range (ml)

Orange button

5 — 40

0.005 — 0.04

Yellow button

40 — 200

0.04 — 0.2

Blue button

200 — 1000

0.2 — 1.0
  1. Firmly push the correct tip on to the end of the pipette.

  2. Dial up the required volume (in microlitres) by twisting the coloured button. N.B. Do not try to dial in a figure above or below the stated volume range or you will jam the pipette. If you need a volume outside the stated range, choose a different pipette.

  3. Holding the pipette by the barrel, push down the button with your thumb to the first position of resistance and hold it there.

  4. Submerge the disposable tip just below the surface of the liquid to be pipetted and gently allow the plunger to rise again by slowly releasing the pressure from your thumb (do not just take your thumb off the end and allow the plunger to shoot up otherwise you will get liquid into the barrel of the pipette). The correct volume of liquid should now be in the tip. Once the plunger has risen fully (and NOT before), remove the pipette tip from the liquid. Check that the volume looks right (this becomes easier with experience) and that there are no air bubbles or air gaps.

  5. Place the tip in the receiving tube (near the bottom and touching against the side) and slowly push down on the plunger with your thumb through the first position of resistance to the second. Remove the pipette from the tube and check that all the liquid is out of the tip.

  6. You can continue to use the same tip if (a) you are pipetting more of the same solution or (b) if you are pipetting dilutions of the same solution as long as you are working from the most dilute to the most concentrated (but NOT the other way round). Otherwise eject the tip into a waste bin by pushing down on the eject slider with your thumb.

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