How To Use Micropipettes

A micropipette is the type of laboratory equipment used for measuring and transferring small volumes (1microliter and less) of liquids. To obtain precise results of an experiment, you should have a deeper understanding of the main micropipettes' features and their operating principles.

1. Three sizes of micropipettes. The sizes are noted on the top of the plunger button. Neither upper nor lower limits should be ever exceeded. The size of an instrument you can find the top of the plunger button.

2. Set the needed volume by turning the centrally located rings clockwise to increase volume or counterclockwise to decrease volume.

P20: Maximum volume is 20 microliters. Accurate between 5 and 20 microliters. Numbers on the micropipette (typically black/black/red) are read as XX.X microliters. The color change indicates the position of the decimal point.

P200: Maximum volume is 200 microliters. Accurate between 20 and 200 microliters. Numbers on the micropipette (one color) are read as XXX microliters.

P1000: Maximum volume is 1000 microliters (= 1 milliliter). Accurate between 200 and 1000 microliters. Numbers on the micropipette (typically red-black-black) are read X.XX milliliter. Note that this micropipette reads milliliters while the other two read microliters.

The example below shows how to read the micropipette:

3. Place a tip on the discharge end of the pipette. If sterile conditions are necessary, you should not let the pipette tip touch any object around or even your hands.

4. While depressing the plunger, it will stop at two different positions. The first stopping position is the point of initial resistance and is the level of depression. It will result in the needed volume of the transferred liquid. This first stopping position is dependent on the volume that is being transferred. That’s why the distance along which you have to push the plunger to reach the point of initial resistance will change depending on the volume being pipetted. The next stopping position you can find when the plunger is depressed beyond the initial resistance until it is in contact with the body of the pipette. At this position, the plunger cannot be further depressed (this second stopping position is used for the complete discharging of liquids from the plastic tip); when drawing liquid into the pipette, you should not reach this second stop, only when expelling the last drop. Try to practice depressing the plunger to each of these stopping positions until you easily distinguish between these points before continuing.

5. Before drawing a liquid in, the tip of a pipette should be put into the liquid just slightly below the surface as shown below.

NOTES:

• Never point a pipette up. This may cause the liquid to run down into the pipette destroying it.
• When withdrawing liquids with the pipette, always release the plunger slowly. This prevents liquid from rushing into the end of the pipette and clogging it up. This is especially important with large volume pipettes (200-1000 microliters).
• Be sure you use the proper size tip for each pipette.
• Always use a new tip for each different liquid.
• Use the correct pipette for the volume that is to be dispensed. Never use the 200-1000 microliters pipette to dispense volumes below 200 microliters. Going below or above the range of the micropipette may damage the instrument.