Pipettes

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Pipettes are crucial for accurate delivery of the small volumes of liquid necessary for biological research and techniques. Delivery generally ranges from 1-1000uL. Never, ever dial a pipette over the maximum volume displayed on the unit. Accurate and reproducible liquid delivery depends on correct technique. Ask for someone who knows what they are doing to spend 10 minutes training you.

Pipettes operate by piston-driven air displacement. A vacuum is generated by the vertical travel of a metal or ceramic piston within an airtight sleeve. As the piston moves upward, driven by the depression of the plunger, a vacuum is created in the space left vacant by the piston. Air from the tip rises to fill the space left vacant, and the tip air is then replaced by the liquid, which is drawn up into the tip and thus available for transport and dispensing elsewhere.

Sterile technique prevents liquid from coming into contact with the pipette itself. Instead, the liquid is drawn into and dispensed from a disposable pipette tip that is changed between transfers. Depressing the tip ejector button removes the tip, that is cast off without being handled by the operator and disposed of safely in an appropriate container. This also prevents contamination of or damage to the calibrated measurement mechanism by the substances being measured.

The plunger is depressed to both draw up and dispense the liquid. Normal operation consists of depressing the plunger button to the first stop while the pipette is held in the air. The tip is then submerged in the liquid to be transported and the plunger is released in a slow and even manner. This draws the liquid up into the tip. The instrument is then moved to the desired dispensing location. The plunger is again depressed to the first stop, and then to the second stop, or 'blowout', position. This action will fully evacuate the tip and dispense the liquid. In an adjustable pipette, the volume of liquid contained in the tip is variable; it can be changed via a dial or other mechanism, depending on the model. Some pipettes include a small window which displays the currently selected volume. The plastic pipette tips are designed for aqueous solutions, and are not recommended for use with organic solvents that may dissolve the plastics of the tips or even the pipettes.