How to use a
Burette and Volumetric Pipettes
- Volumetric pipettes labeled
TD (to deliver) at the upper end are designed to deliver the volume stated
on the pipette. There will always be a small amount of liquid inside the tip
after pipetting. If this liquid is blown out you will have delivered
slightly more than the designed capacity of the pipette. Almost all of our
pipettes are TD pipettes. However, other types do exist: Pipettes labeled
TC (to contain) are designed to contain the volume stated on the pipette.
Therefore, all liquid on a TC pipette should be expelled to obtain the
- If a drop of liquid hangs on
the outside tip of the pipette the pipette tip should be dipped into the
solution that has been pipetted to remove this drop. If this is not done
you will have pipetted slightly less that the intended volume.
- Volumetric pipettes, if clean
and used properly, are precise to 0.01 mL. i.e. a 25 ml pipette delivers
25.00 mL, while a 20 mL pipette delivers 20.00 mL
- How to rinse a pipette:
- Fill about half
full with D.I. water.
- Rotate the pipette
while holding it horizontally. Be sure that the water makes contact with
all sides. Discard the water.
- Repeat the previous
two steps with the liquid to be pipetted.
- Pipettes are clean
if no liquid sticks to the sides after pipetting is completed. If
sticking occurs the pipette must be returned for cleaning by the lab
When finished, always rinse/wash the pipette with D.I. at least two to
three times before returning it to the pipette container (contains a glass
detergent) by the front deskódo NOT return a used/wet pipette to the container
from which you got it.
Burettes are designed to deliver any precisely measured
volume of liquid up to the maximum of the buret capacity. Burettes have scale
divisions of 0.1 mL. Estimates between scale divisions can be made. Therefore,
all volumes should be recorded to the nearest 0.01 mL (e.g. 22.48 mL, 20.00 mL,
15.60 mL, etc.)
How to rinse a burette:
Rinse the buret two to three times with about
15-10 rnL of D.I. water. Be sure that all inner sides make contact with the
water. Run some of the water through the tip into a beaker to rinse the tip and
stopcock. Discard the rinse water.
Rinse the buret twice with about 5-10 mL of the
solution to be titrated. Be sure that all inner sides make contact with this solution.
Run some of the water through the tip into a beaker to rinse the tip and
stopcock. Discard the rinse solution into the proper waste container.
A buret is clean if no liquid sticks to the
sides after releasing liquid. If sticking occurs the buret must be returned for
cleaning by the lab technician.
3. How to fill a burette:
- Use a clean and dry
funnel to fill a rinsed buret to about the 0.00 mL mark with the solution
to be titrated.
- To expel air from the
tip and stopcock, run some of the solution out into a small beaker. Tap
the tip to dislodge air while letting the solution out. If the beaker is
not clean and dry discard this solution in the proper waste container.
- Fill the burette
somewhere between the 0.00 and 5.00 mL marks. Record this volume.
- Do not leave the
funnel in the buret since liquid can drip down to give an inaccurate
- Now the buret is ready
4.† When finished, always rinse
the buret with Dl. at least two to three times before returning it.