Air Displacement Pipette

Laboratory pipettes can function either via air displacement or by positive displacement principles.

Air displacement pipette.

These pipettes operate by piston driven air displacement. Air displacement pipette used for standard pipetting applications is highly accurate. In an air displacement pipette an air cushion separates the liquid in the plastic tip from the piston inside the pipette. Due to its high accuracy this laboratory tool is commonly used in standard pipetting applications.

In air displacement pipettes a certain volume of air remains between the piston and the liquid. As the piston moves upward driven by the depression of the plunger a vacuum is created in the space left vacant by the piston. Both pipette types have a piston that moves in a cylinder or capillary. The liquid s density influences the size of air cushion e g.

When using positive displacement pipettes there is no elastic air space to expand or contract so the aspiration force remains constant unaffected by the physical properties of the sample. When enabled the pressure is monitored in the tip. Zeus is equipped with anti droplet control adc. These liquids tend to vaporize in the tip which raises the air pressure resulting in liquid dripping from the tip.

Acids bases and solvents are the worst enemies of any air displacement pipette. A vacuum is generated by the vertical travel of a metal or ceramic piston within an airtight sleeve. However conditions such as temperature atmospheric pressure as well as the specific gravity and viscosity of the solution may have an effect on the performance of air displacement pipettes. Unlike an air displacement pipette which dispenses liquid using an air cushion in the pipette tip the piston in a positive displacement pipette makes direct contact with the sample allowing the aspiration force to remain constant.

In positive displacement pipetting the piston is in direct contact with the liquid. Too low too high volume is pipetted. Adjust pipette to liquid becomes fixed volume pipette for adjusted volume. No air cushion therefore no problem.

Volatile liquids like acetone and methanol can be extremely difficult to pipette using air displacement.