Air displacement pipette

Piston-driven air displacement pipettes are a type of micropipette, which are tools to handle volumes of liquid in the microliter scale.

Normal operation consists of depressing the plunger button to the first stop while the pipette is held in the air.

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.

This is important because accuracy decreases when the set volume is close to the pipette's minimum capacity.

These tips have a little piece of foam plastic in the upper conus to prevent sample aerosols contaminating the pipette.

The spacing of tips in these boxes is usually standardised for multichannel pipette compatibility from a number of different suppliers.

For manual high-throughput applications like filling up a 96-well microtiter plate most researchers prefer a multi-channel pipette.

Some pipettes, however, feature dials for setting the individual volume digits that can only be adjusted when unlocked by depressing and twisting the plunger.

For sustained accuracy and consistent and repeatable operation, pipettes should be calibrated at periodic intervals.

These intervals vary depending on several factors: Under average conditions, most pipettes can be calibrated semi-annually (every six months) and provide satisfactory performance.

This entails dispensing samples of distilled water into a receiving vessel perched atop a precision analytical balance.

Relative humidity, ambient temperature, and barometric pressure are factors in the accuracy of the measurement, and are usually combined in a complex formula and computed as the Z-factor.

This Z-factor is then used to modify the raw mass data output of the balance and provide an adjusted and more accurate measurement.

The colorimetric method uses precise concentrations of colored water to affect the measurement and determine the volume dispensed.

It is also recommended for extremely low-volume pipette calibration, in the 2 microliter range, because the inherent uncertainties of the gravimetric method, performed with standard laboratory balances, becomes excessive.

Properly calibrated microbalances, capable of reading in the range of micrograms (10−6 g) can also be used effectively for gravimetric analysis of low-volume micropipettes, but only if environmental conditions are under strict control.