When scientists need to accurately and precisely deliver smaller volumes of a liquid, they use a pipette – a calibrated glass tube into which the liquid is drawn and then released.  Glass and plastic pipettes have been mainstays of chemistry and biology laboratories for decades, and they can be relied upon to dispense volumes down to 0.1mL.

Molecular biologists frequently use much smaller volumes of liquids in their work, even getting down to 0.1µL (that’s one ten thousandth of a millilitre, or one ten millionth of a litre!).  For such small volumes, they need to use a micropipette.

Micropipette

Micropipettes are called a lot of different names, most of which are based on the companies which manufacture. For example, you might hear them called “Gilsons”, as a large number of these devices used in laboratories are made by this company. Regardless of the manufacturer, micropipettes operate on the same principle: a plunger is depressed by the thumb and as it is released, liquid is drawn into a disposable plastic tip. When the plunger is pressed again, the liquid is dispensed.

The tips are an important part of the micropipette and allow the same device to be used for different samples (so long as you change your tip between samples) without washing. They come in a number of different sizes and colours, depending on the micropipette they are used with, and the volume to be dispensed.

The most commonly used tips are:

Large Blue – 200-1000µL

Small Yellow – 2-200µL

Small White - <2µL

They are loaded into tip boxes which are often sterilized to prevent contamination. For this reason tip boxes should be kept closed if they are not in use. Tips are loaded onto the end of the micropipette by pushing the end of the device into the tip and giving two sharp taps. Once used, tips are ejected into a sharps disposal bin using the tip eject button. Never touch the tip with your fingers, as this poses a contamination risk.

 

 

 

The plunger can sit at any one of three positions: 

Position 1 is where the pipette is at rest

Position 2 is reached by pushing down on the plunger until resistance is met

Position 3 is reached by pushing down from position 2

Position 1 of a micropipette Position 2 of a micropipette Position 3 of a micropipette

Each of these positions play an important part in the proper use of the pipette. 

 

To Draw Up Liquid

To remove the last drop of liquid from the tip, push down to Position 3. If delivering into a liquid, remove the tip from the liquid before releasing the plunger

Hold the micropipette with the thumb resting on the plunger and the fingers curled around the upper body. 

Push down with the thumb until Position 2 is reached.

Keeping the plunger at the second position, place the tip attached to the end of the micropipette beneath the surface of the liquid to be drawn up. Try not to push right to the bottom (especially if you are removing supernatant from a centrifuged pellet), but ensure that the tip is far enough below the surface of the liquid that no air is drawn up.

Steadily release pressure on the plunger and allow it to return to Position 1. Do this carefully, particularly with large volumes, as the liquid may shoot up into the tip and the body of the micropipette. If bubbles appear in the tip, return the liquid to the container by pushing down to Position 3 and start again (you may need to change to a dry tip).

To draw up liquid, step 1 To draw up liquid, step 2 To draw up liquid, step 3

 

To Dispense Liquid

Hold the micropipette so that the end of the tip containing tip is inside the vessel you want to deliver it to. When delivering smaller volumes into another liquid, you may need to put the end of the tip beneath the surface of the liquid (remember to change the tip afterwards if you do this to save contaminating stock). For smaller volumes you may also need to hold the tip against the side of the container. 

Push the plunger down to Position 2. If you wish to mix two liquids together or resuspend a centrifuged pellet, release to Position 1 and push to Position 2 a few times to draw up and expel the mixed liquids

To remove the last drop of liquid from the tip, push down to Position 3. If delivering into a liquid, remove the tip from the liquid before releasing the plunger

Release the plunger and allow it to return to Position 1

Expelling liquid from a micropipette, step 1 Expelling liquid from a micropipette, step 2 Expelling liquid from a micropipette, step 3

 

Changing the Volume

Some micropipettes deliver fixed volumes, however the majority are adjustable. Each brand uses a slightly different method to do this – Gilsons have an adjustable wheel, others have a locking mechanism and turning the plunger adjusts the volume. All have a readout which tells you how much is being delivered and a range of volumes which can be dispensed. Trying to dipense less than the lower value of the range will result in inaccurate measurements. Trying to dispense over the upper range will completely fill the tip and allow liquid to enter the body of the pipette. Do not overwind the volume adjustment, as this affects the calibration of the micropipette.  

The way to interpret the readout depends on the micropipette used:

Changing the volume on a P1000 micropipette

In a 200-1000µL micropipette (e.g. a Gilson P1000) the first red digit is thousands of µL (it should never go past 1), the middle digit is hundreds, while the third is tens. Therefore 1000µL would read as 100, while 350µL would read as 035.

Changing the volume on a P200 micropipette  

In a 20-200µL micropipette (e.g. a Gilson P200) the first digit is hundreds of µL (it should never go past 2), the second is tens and the third is units. Therefore 200µL would read as 200, while 95µL would read as 095.

Changing the volume on a P20 micropipette

In a 2-20µL micropipette (e.g. a Gilson P20) the first digit is tens of µL (it should never go past 2), the second is units and the third red digit is tenths. Therefore 20µL would read as 200, while 2.5µL would read a 025

Changing the volume on a P2 micropipette

In a 0.2-2µL micropipette (e.g. a Gilson P2) the first digit is units of µL (it should never go past 2), the second red digit is tenths and the third red digit is hundredths. Therefore, 2µL would read as 200, while 0.5µL would read as 050

 

GENIE at The University of Leicester has an excellent video showing how to use micropipettes here (note: this opens to You Tube - it may not be available to some users).