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Gilson micropipettes are one of the most commonly used instruments in a molecular biology laboratory. They're used in conjunction with plastic, disposable pipette tips to measure or transfer small amounts of liquids, usually from 0.2 microliters to 1000 microliters, or one milliliter. Different pipettes work across different ranges of volumes and are named by the maximum volume they pipette. The different pipettes look very similar, so they're labeled on the top of each push button with a capital P followed by a number, which indicates the maximum volume for that particular pipette. A P2 pipettes between 0.2 and 2 microliters; a P20 pipettes between 2 and 20 microliters; a P200 pipettes between 20 and 200 microliters; and a P1000 pipettes between 100 and 1000 microliters.
A pipette is an expensive, precision instrument; improper use will damage the pipette, so correct use is essential. You should never use a pipette to measure volumes outside of its range. For example, using a P20 pipette to measure lower volumes, such as 10 microliters, or to higher volumes, such as 250 microliters, will result in inaccurate volume measurements and will damage the internal mechanism of the pipette.
Each pipette has a vertical row of three numbers visible in the body of the instrument. To set the volume, you can use either the thumb wheel or, on newer models, the push-button. This will cause the three number dials in the body of the pipette to rotate and change the volume of liquid that will be taken up. However, the dial numbers indicate different volumes depending on which pipette is used. For example, these three pipettes have been set to read the same numbers on the dial: 152. For the P2, this means that the pipette is set to a volume of 1.52 microliters; the bottom two dials are in red, indicating five-tenths and two-hundredths of a microliter. For the P20, this means that the pipette is set to a volume of 15.2 microliters; the red bottom dials show two-tenths of a microliter. With the P200, the same visual setting means that the pipette is set to a volume of 152 microliters. This P1000 is set to 052, which indicates a volume of 520 microliters. A setting of 100 indicates the maximum volume for this pipette, which is 1000 microliters; the uppermost number is in red, which for this pipette indicates the number of milliliters.
Once you've set the volume you need, attach the appropriate pipette tip to the end of the pipette. P20 and P200 pipettes use the same yellow tips; P1000 pipettes use larger blue tips. Another type of tip, called a filter tip, is often used in the laboratory. The sterile filter within each tip can help to prevent contamination.
Hold the pipette with one hand, with the narrow side resting in the palm of the hand. Add the pipette tip by gently but firmly pushing the pipette into the pipette tip, which is held in a tip box. You may need a little practice to learn to apply the right amount of pressure to give a good airtight seal between the tip and the pipette. Liquid is drawn in and expelled using the pipette's plunger. Gently apply pressure to the button with your thumb until you feel a natural stop; this is called the first stop. The distance you need to push the push button down will vary depending on the volume you require. A P20 set to 2 microliters will require less push-button movement than a P20 set to 20 microliters.
So, to use the pipette, push the button down to the first stop. Then, keeping the push button at this level, place the pipette tip about two millimeters into the liquid you wish to draw up. Release the push button by slowly allowing it to return to its original position. Pause for a second to make sure all the required volume of liquid has been taken up into the tip. This is especially important when using more viscous liquids, which take longer to draw up. Withdraw the pipette tip from the liquid and place it inside the recipient container. Slowly push down on the push button; this will release the liquid in the pipette tip into the tube. This time, push beyond the first stop; this ensures that any residual liquid is expelled from the pipette tip. Fully withdraw the pipette tip from the liquid before you release the push-button.
So to recap: push down the push button until you feel some resistance; place the pipette into the liquid and slowly release the push button; release the liquid from the pipette by pushing past the first stop to fully expel the liquid from the pipette tip into the recipient container; withdraw the pipette from the container before you release the button. For very small volumes, the aspirated liquid can hang in a drop from the end of the tip and may not be transferred to the tube at all, so you should touch the tip to the inside wall of the recipient container whilst expelling the liquid.
Once you've aspirated the liquid, release the pipette tip from the pipette by pressing down on the tip ejector; this is the small white button at the top of the main body of the pipette. Be sure that the attached pipette tip is inside the appropriate waste container before pressing the tip ejector. A new, clean pipette tip should be used with each new liquid, or if the tip touches any surface or any liquid other than the one you're pipetting. If in doubt, change the tip. Do not use a pipette without a tip attached. Liquid should never enter the body of the pipette; it will cause the pipette to corrode and will be a major source of contamination between liquids and experiments. Do not use a pipette past its volume limits; this causes pipetting inaccuracies and also damages the pipette.
If you're having trouble attaching a tip to your pipette, don't repeatedly jam the pipette into a tip; this can damage the pipette. If the tip doesn't stay on the end of the pipette, simply repeat the procedure with a new tip. When pushing down the push-button to take up a set volume of liquid, don't push past the first stop; if you push past the first stop, the volume you then take up will be too large. When taking up liquids, don't simply let go of the push button; the liquid can be sprayed around the inside walls of the tip and up into the pipette body, causing inaccurate volume dispensing and pipette contamination. Make sure you release the push button in a controlled manner. If you don't pause after you release the push button, there won't be enough time for the correct volume to be taken into the tip; air will be taken in instead. Also, when you're withdrawing a large volume from a narrow container, make sure the tip stays below the surface. Whenever you have liquid in a pipette tip, don't lay the pipette down; liquid can get into the body of the pipette, which causes cross-contamination, pipette damage, and inaccurate pipetting. And finally, remember when pipetting small volumes, touch the pipette tip to the side of the tube to ensure the liquid is released into the recipient container.