Pipettes and it's types

Pipettes

These are used to transfer a known volume of liquid from one container to another. They are designed either to contain (TC) a specific volume of liquid or to deliver (TD) a specified volume. 

To contain and To deliver (TC & TD): Manufacturer stamp TC or TD near the top of the pipet. TC pipet holds or contains a particular volume but does not dispense that exact volume, whereas TD pipet will dispense that exact volume indicated.

(Source: Bishop's Clinical chemistry, 5th Ed)

Blowout and self-draining: A blowout pipet has continuous etched ring or two small, close continuous rings located near the top of the pipet. This means that the last drop of liquid should be expelled into the receiving vessel. Without these markings, a pipet is self-draining, and content of pipet drain by gravity.

Transfer pipettes: It transfers a known volume of liquid without further subdivisions. They include both volumetric and Ostwald-Folin pipettes. They consist of a cylindrical bulb joined at both ends to narrower glass tubing. A calibration mark is etched around the upper suction tube. The bore of delivery orifice should be sufficiently narrow to prevent rapid outflow of liquid and incomplete drainage.

A volumetric transfer pipett is calibrated to deliver accurately a fixed volume of a dilute
aqueous solution. Ostwald-Folin pipettes have bulb closer to the delivery tip unlike volumetric pipett which has at center. These (OF) are used for accurate measurement of viscous fluids, such as blood or serum. In contrast to volumetric pipett, an Ostwald-Folin pipett has an etched ring near the mount piece, indicating it is a blow out pipett. With the use of pipetting bulb, liquid is blown out of the pipett only after blood or serum has drained to the last drop in delivery tip. Volumetric pipet are self draining and is used in diluting standards, calibrators, or quality-control materials.

Measuring pipettes: These are graduated or measuring pipette and can dispense different volumes as these have many graduations. It has uniform graduations along its length. Two kinds are available; the Mohr pipette has graduations ends above the tip and serological pipette has graduated marks down to the tip. Mohr pipet is self draining. The serological pipette must be blown out to deliver the entire volume of the pipette and has an etched ring (or pair of rings) near the bulb end of the pipette signifying that it is a blow-out pipette. Serological pipettes have a larger orifice than do the Mohr pipettes and thus drain faster. Measuring pipettes are used for the transferring and measurement of reagents and making dilutions and are not considered sufficiently accurate for measuring samples and calibrators. Micropippet is also a measuring pippet which can measure less than 1mL. 

Micropipettes: 

These are pipettes to measure micro liter of volume. Inner wall of pipette can be coated with liquid so most micropipettes are calibrated to contain (TC) that stated volume rather than to deliver it.

Semiautomated and automatic pipettes: These are programmable pipets that can automatically take up the specified volume and can dispense in multiple wells at same time. There are 3 types’ air-displacement, positive-displacement and dispenser pipets.