The dispensing of small volumes of liquids with a high accuracy and repeatability is a routine operation in the bioscience laboratory. The equipment used for this purpose are costly precision instruments, which require careful handling. You will use the Gilson Pipetman® or the Labnet Biopette®, which allow one to deliver volumes down to 0.1 µl. The information below is adapted from the Gilson Pipetman manual. The operation of the Labnet Biopette is very similar.
The Gilson Pipetman
The Pipetman®, shown above, is a volumetric instrument designed to measure and transfer liquids precisely and safely. Eight different models are available, which cover a volume range from 0.1 μl to 10 ml
A diagram of the outer features of the Pipetman is shown on the left. The labels A-F refer to:
A: The push button (which is labelled with the maximum volume for the instrument).
B: A knurled knob by means of which the volume to be delivered may be adjusted. The volume is read on a digital volumeter.
C: The shaft, which may be autoclaved at for 20 minutes at 120 °C and 1 bar pressure. Do not attempt to dismantle the Pipetman! Get a staff member to assist you!
D: Disposable tip ejector (not found on P5000 and P10ml). This is activated by pressing on the button E.
F: Disposable polypropylene tip.
Setting the volume
The volumeter consists of three numbers, and is read from top to bottom. The three numbers indicate the number selected. Note that the sequence of number indicate different volumes for each model.
The volume of the pipette is set by turning the black knurled adjustment ring (marked B in the above diagram).
To obtain maximum accuracy when changing the volumeter setting, follow the recommendations below:
- When decreasing the volume setting, turn the adjustment ring slowly to reach the required setting, making sure not to overshoot the mark.
- When increasing the volume setting, turn the adjustment ring until you are about1/3 turn above the required setting. Turn the adjustment ring slowly to decrease the volume to reach the desired setting, making sure not to overshoot the mark.
Place a suitable tip on the shaft of the pipette. Press the tip on firmly using a slight twisting motion to ensure a positive, airtight seal. Never handle a liquid with a Pipetman that has not been fitted with a tip.
- Press the push button to the first positive stop (diagram A above).
- Holding the pipette vertically, immerse the tip into the sample liquid. The depth to which the tip should be immersed in the sample liquid depends on the model
- P2 and P10: 1 mm
- P20 and P100: 2-3 mm
- P200 and P1000: 3-6 mm
- P5000: 3-6 mm P10ml: 5-7 mm
- Release the pushbutton slowly and smoothly to aspirate the sample (diagram B above).
- Wait one second and then withdraw the tip from the liquid. Wipe any droplets away from the outside of the tip using a tissue. Avoid touching the orifice of the tip..
- Place the end of the tip against the inside wall of the vessel at an angle of 10 to 40 degrees. Press the pushbutton smoothly to the first stop (diagram C above). Wait one second. Press the pushbutton to the second stop to expel any remaining liquid (diagram D above).
- Keeping the pushbutton pressed to the end, remove the pipette by drawing the tip along the inside surface of the vessel.
- Release the pushbutton (diagram E above).
- Eject the tip by pressing the ejector button. It is only necessary to change the tip if a different liquid is being sampled or if the volumeter setting is changed.
When pipetting liquids that have a viscosity and density different to water, for example, organic solvents, a film of liquid is formed on the inside wall of the pipette tip. The film can create an error. Since the film remains relatively constant in successive pipetting operations with the same tip, this error can be avoided by forming the film before dispensing the first sample. This is done by aspirating a sample and dispensing it into the same vessel. Since the film is already formed, all the following samples will have better accuracy and repeatability.
Typical Volumeter Reading
|0.1 – 2 μl
|Measurement and transfer of micro-volumes, DNA sequencing and enzyme assays
|0.5 – 10 μl
|2 – 20 μl
|Measurement and transfer of general aqueous solutions, acids and bases.
|20 – 100 μl
|50 – 200 μl
|200 – 1 000 μl
|1 – 5 ml
|Measurement and transfer of large volumes.
|1 – 10 ml
The Gilson polypropylene tips are chemically clean and may be autoclaved at 120 °C for 20 minutes at 1 bar pressure.
They come in different colours, as indicated in the table below… Note: The colour of the top of the pushbutton of the Pipetman corresponds to the colour of the tip that should be used.
For Pipetman model
|0.1 μl – 10 μl
|P2 – P10
|2 μl – 200 μl
|P20 – P100
|200 μl – 1 ml
|1 ml – 5 ml
|1 ml – 10 ml