PositiveDisplacementPipetten

Positive displacement pipettes are laboratory tools used to transfer precise volumes of liquids. Unlike air displacement pipettes, which create a vacuum using an air cushion, positive displacement pipettes directly contact the liquid with a disposable piston or plunger. This direct contact ensures accurate dispensing of viscous, volatile, or dense liquids that might be problematic for air displacement pipettes.

The mechanism involves a disposable tip, often resembling a syringe, containing a plunger. When the plunger is retracted, it creates a vacuum that draws the liquid directly into the tip. When the plunger is advanced, it pushes the liquid out. This direct displacement eliminates the air gap and the associated inaccuracies.

Positive displacement pipettes are particularly useful for handling liquids with high viscosity, such as oils or glycerol, and volatile liquids like acetone or ether, where evaporation can affect the air cushion in other pipette types. They are also favored for dispensing dense solutions. The disposable nature of the tips prevents cross-contamination and ensures accuracy for each measurement. Different sizes of positive displacement pipettes are available, corresponding to specific volume ranges, and the calibration of these pipettes is crucial for reliable results in scientific applications.