The micropipettor is used to transfer small amounts (< 1 ml) of liquids. The scales on micropipettors are in microliters (1000µl = 1 ml). The brand of micropipettors we will be using is made by Rainin and called a "Pipetman". They come in three sizes which are capable of pipetting three ranges of volumes: P20 = 0.5- 20 µl, P200 = 20-200 µl, and P1000 = 200-1000 µl. They are used in conjunction with disposable (often sterile) plastic tips; the smaller two micropipettors (P20 and P200) require the yellow tips and the P1000 pipettor uses the larger blue tips. The following is an illustration of a micropipettor:
3. Place a tip on the discharge end of the pipettor. NOTE: If sterile conditions are necessary do not allow the pipet tip to touch any object (including your hands).
4. The plunger will stop at two different positions when it is depressed. The first of these stopping points is the point of initial resistance and is the level of depression that will result in the desired volume of solution being transferred. Because this first stopping point is dependent on the volume that is being transferred, the distance you have to push the plunger to reach the point of initial resistance will change depending on the volume being pipetted. The second stopping point can be found when the plunger is depressed beyond the initial resistance until it is in contact with the body of the pipettor. At this point the plunger cannot be further depressed. This second stopping point is used for the complete discharging of solutions from the plastic tip. You should not reach this second stop when drawing liquid into the pipettor, only when expelling the last drop. Before continuing, practice depressing the plunger to each of these stopping points until you can easily distinguish between these points.
5. Depress the plunger until you feel the initial resistance and insert tip into the solution, just barely below the surface of the liquid and not as deep as possible.
6. Carefully and slowly release
plunger. NOTE: If the solution you are pipetting is viscous, allow
the pipet tip to fill to final volume before removing it from
solution to avoid the presence of bubbles in the plastic tip which
will result in an inaccurate volume.
7. Discharge the solution into the appropriate container by depressing plunger. This time, depress the plunger to the point of initial resistance, wait one second, and then continue pressing the plunger as far as it will go in order to discharge the entire volume of solution.
8. Remove tip by pressing down on the tip discarder.
REMEMBER TO CHANGE TIPS BETWEEN SOLUTIONS TO AVOID MIXING OR
CONTAMINATING THE SOLUTIONS USED!!
DOUBLE DIPPING IS PUNISHABLE BY EARLY SATURDAY AND SUNDAY MORNING PHONE CALLS!
© Copyright 2000 Department of Biology,
Davidson College, Davidson, NC 28036
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