Glass Pipettes- Types, Function and Correct Operation

Glass pipettes are also used to deliver liquid of certain volumes and are calibrated at 20 C. There are two main types of glass pipettes commonly used in a clinical laboratory: measuring pipette and transfer pipette.

• Measuring pipettes deliver multiple volumes and are used when less accuracy of measurement is required, such as for delivering reagents or small amounts of solvent. This type of pipette should not to be used for making standard solutions or quality control materials. Examples of measuring pipettes are serological and Mohr pipettes.
• Transfer pipettes deliver one volume and are used when a higher degree of accuracy required. A class A transfer pipette is accurate to within 0.1%. This type of pipette is used for preparation of standard solutions to be used in calibration. Transfer pipettes resemble measuring pipettes except that only one measurement mark appears on the neck and there is a round or cylindrical bulb toward the middle or base of the pipette. Types of transfer pipettes include standard volumetric pipettes, Ostwald-Folin pipettes, and automated micropipettes.

Proper/ Correct Operation of a Glass Pipette

1. Place a mechanical suction bulb or device on the top of the glass pipette.
2. Insert the glass pipette into the fluid to a level that will aspirate fluid and not air bubbles.
3. Aspirate the fluid above the desired total volume by depressing the suction bulb, taking care not to aspirate it up into the bulb.
4. Remove the bulb, placing your finger over the top of the glass pipette.
5. Wipe off the outside of the pipette with gauze, taking care not to wipe the bottom, which could wick away fluid from inside the pipette.
6. Adjust the meniscus: read the meniscus at the bottom of the curve of the liquid.
7. Drain the liquid into the receiving vessel.
8. Place the suction bulb on the top of the pipette and blow out the last drop into the receiving vessel if this is a graduated pipette that calls for dispensing the last drop.