Pipettors and Tips
Pipettes and tips are used for accurate liquid handling in many lab applications. This area includes both pipettors, which are complete devices used to deliver a known quantity of solution to a vessel; and pipette tips, through which fluids are dispensed, which are often sold separately from the pipette or pipettor. Pipettes and tips are either of the classical style (glass) or digital.
There are three main types of pipettes and tips: positive displacement, air displacement, and Pasteur styles. Pasteur pipettes are small glass tubes with a bulb at the end used for dispensing small amounts of fluids. Positive displacement pipettes are used for high viscosity and volatile liquids. Both types of pipettes have a piston that moves in a cylinder, or capillary. In air displacement pipetting, a specified volume of air remains between the piston and the liquid. In positive displacement pipetting, the piston is in direct contact with the liquid.
Selecting air displacement pipettes and tips require special consideration. Air displacement pipetting, which is used for standard pipetting applications, is highly accurate. Even so, conditions such as atmospheric pressure, and the specific gravity and viscosity of the solution can have an effect on the performance of air displacement pipettes. Typically, air displacement pipettes are meant for general use with aqueous solutions.
Positive displacement pipettes and tips are used in applications that require extreme accuracy. These pipettes and tips are also recommended for specialized procedures such as DNA amplification. The microsyringe tips used in positive displacement pipettes are disposable, which helps avoid sample-to-sample and cross-contamination, and contamination due to the aerosol effect. Positive displacement pipettes and tips are also used for high viscosity and volatile liquids.
