Common different types of pipettes include five different types: air displacement pipettes, positive displacement pipettes, volumetric pipettes, graduated pipettes, and Pasteur pipettes.
An air displacement pipette, also known as a "displacement pipette gun," is an adjustable, microliter volume measuring pipette used to measure volumes from 0.1-1000 μL. This type of pipette requires a disposable tip that contacts the liquid.
The air displacement pipette operates by using a piston to expel air, which produces a vacuum in the closed cylinder. When the piston is pulled up, the back half of the gas is compressed, while the front half of the space becomes a vacuum. The liquid near the tip of the pipette enters the vacuum, and can then be transferred or dispensed. This type of transfer pipette has high accuracy and precision, and is suitable for routine pipetting.
However, because it relies on the movement and compression of gas, the accuracy is greatly affected by environmental conditions, especially temperature, pressure, and the user's technique. Therefore, this device must be properly stored and calibrated, and the user must be trained and practice correct and stable operating techniques.
Among different types of pipettes, this type of pipette is similar to the air displacement pipette, but is less commonly used. It is usually used to prevent contamination, or for small volumes of volatile or viscous substances, such as volatile organic compounds, DNA, etc. The disposable tip of the positive displacement pipette is a micro-adjustable syringe with a plastic piston that contacts the liquid directly.
Volumetric pipettes, also known as "transfer pipettes," have extremely high precision (four significant figures). These pipettes have a spherical object with a scale line above it, which only marks the fixed volume of the pipette. Typical volumes are 10, 25, and 50 mL. Volumetric pipettes are commonly used to prepare solutions from basic materials, or for the preparation of titration liquid.
Graduated pipettes, also known as graduated pipettes or graduated transfer pipettes, are long glass tubes with a series of graduated lines that can be used to suck up different amounts of liquid. These graduated pipettes typically have volumes of 5, 10, 25, or 50 mL. Graduated pipettes have a positive and negative error range, which is between 0.6% and 0.4% of the theoretical volume when measured at 20℃. Graduated pipettes are manufactured according to ISO precision and scale layout standards. Type A precision is higher than Type B precision.
Pasteur pipettes are plastic or glass pipettes used for transferring small amounts of liquid, but are not marked with any volume graduations or lines. Pasteur pipettes are more commonly known as droppers or chemical droppers.