AP Lab 02 - Biology Lab Skills

Name: ______________________________ AP Biology – Lab 02
Micropipeting and Microquantity Measurement
This part of the lab introduces sterile pipeting and micropipeting techniques used often in
molecular and microbiology protocols. Mastery of these techniques will be important for good
results in these applications. Most microchemical protocols involve very small volumes of DNA
and other reagents. These require you to use an adjustable micropipette that measures as little
as one microliter (L) a millionth of a liter, compared to millileters (mL) which are only one
thousandth of a liter.
Using a Glass Pipette
Take a 10 mL glass (or nalgene) pipette. Carefully place
the attachment of the three-way bulb (Figure 1) over the
mouth of the pipette. Squeeze the air valve (A) and the
bulb simultaneously to empty the bulb of air. Place the tip
of the pipette below the solution's surface in the beaker.
Gradually squeeze the suction valve (S) to draw liquid into
the pipette. When the liquid is above the specified volume,
stop squeezing the suction valve (S). Do not remove the
bulb from the pipette.
DO NOT ALLOW LIQUID TO ENTER THE PIPETTE
BULB. If the level of the solution is not high enough,
squeeze the air valve (A) and the bulb again to expel the air from the bulb. Draw up more
liquid by squeezing the suction valve (S). If the level of the solution is above the specified
volume (or 0.00 mL in a TD pipette), gently squeeze the empty valve (E) so the meniscus is
at the correct mark.
Touch the tip of the pipette to the inside of the beaker to remove the drop hanging from
the tip. If this drop is not eliminated, the volume transferred will be slightly higher than the
volume desired.
To transfer the solution into the desired vessel, press the empty valve (E) until the meniscus
is at the mark corresponding to the appropriate volume. Touch the tip of the pipette to the
wall of the receiving vessel to remove any liquid from the outside of the tip. Record the final
volume in the pipette. The volume transferred is equal to the final pipette reading minus the
initial pipette reading.
Procedure 7:
The accuracy of glass pipette measurements
1. Using a 400 gram top-loading balance, tare a dry 250 mL beaker.
2. Using a 10 mL glass pipette and pipette bulb, as carefully as possible, measure 10 mL of
de-ionized (DI) water.
3. Dispense this measured amount of water into the 250 mL beaker.
4. Record the mass of the water to the nearest 0.01 g in Table 7.
5. Tare the balance.
6. Again, using the 10 mL glass pipette, measure 10 mL of water and add it to the 250 mL
beaker.
7. Record the mass in Table 7.
8. Repeat this procedure until you have 50 mL of water in the beaker on the balance.
9. Calculate the error columns in Table 7.
Figure 1: Diagram of a pipette bulb.
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