Air Displacement Micropipettes: As the name suggests, the air displacement micropipette usually functions on the principle of air displacement. It has a piston that dispenses and aspirates liquid samples every time the air pockets travel up and down. Air displacement micropipettes are a type of adjustable micropipette that deliver a measured volume of liquid; depending on size, it could be between about 0.1 µl to 1,000 µl (1 ml). These pipettes require disposable tips that come in contact with the fluid.
Positive Displacement Pipettes: These are similar to air displacement pipettes, but are less commonly used and are used to avoid contamination and for volatile or viscous substances at small volumes, such as DNA. The major difference is that the disposable tip is a microsyringe (plastic), composed of a capillary and a piston (movable inner part) which directly displaces the liquid.