Air-displacement pipettes: air cushion vs liquid contact
An air-displacement pipette moves a piston that displaces an air column. That air cushion draws and delivers liquid. It is the default mechanism on most adjustable laboratory micropipettes.
How the air cushion works
Depressing the plunger moves an internal piston. When the plunger is released, the piston rises and air is displaced, so liquid enters the tip. The calibrated volume is the air volume, not a piston that touches the sample.
Because an air column sits between piston and liquid, temperature, humidity, tip seal, and liquid vapor pressure all affect delivered volume. That is why technique (pre-wetting, immersion depth, pause) matters on these instruments.
When air displacement is the usual choice
Air-displacement pipettes are the routine tool for aqueous buffers, dilute acids/bases, and other water-like liquids. Forward pipetting (aspirate to the first stop, dispense through the second stop) is the standard method for those liquids.
Air displacement vs positive displacement
| Point | Air displacement | Positive displacement |
|---|---|---|
| What moves the liquid | Air cushion above the sample | A piston/capillary that contacts the liquid |
| Typical use | Aqueous, routine volumes | Viscous, volatile, or dense liquids where an air cushion is unreliable |
| Consumable | Standard disposable tip | Usually a dedicated capillary/piston tip |
This page does not rank a “best” positive-displacement model. Specify the liquid class, volume, and sterility in an RFQ if you need NIITO to source a matching pipette and tip system.
Buying notes without invented specs
Ask for volume range, single- vs multi-channel, autoclaveable lower part if required, and tip compatibility. Do not assume one tip family fits every pipette body.
Related pipette pages
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Send volume range, tip type, and quantity. NIITO replies on the RFQ — manufacturer contacts stay off this page.
FAQ
Most adjustable air-cushion micropipettes are. Positive-displacement systems exist as a separate class for difficult liquids.
Not always. Reverse pipetting on an air-displacement pipette is the first technique change. Positive displacement is for cases where an air cushion still fails.