Pipette: Principle, Parts, Types, Procedure, Uses, Examples

Pipettes are indispensable tools in laboratories, widely used for measuring and transferring small volumes of liquids with precision. Their design and functionality have evolved over time, making them essential for various scientific applications. This article delves into the principles behind pipettes, their components, types, procedures for use, and practical applications.

Principle of Pipettes

The functioning of a pipette is primarily based on two mechanisms: air displacement and positive displacement.

• Air Displacement: This is the most common mechanism used in standard pipettes. When the user presses the plunger, air is expelled from the pipette tip, creating a vacuum that draws liquid into the tip when released. The volume of liquid aspirated corresponds to the distance the plunger is pulled down.
• Positive Displacement: In this method, a piston directly displaces the liquid without relying on air pressure. This is particularly useful for viscous or volatile liquids where air displacement might not provide accurate results.

Parts of a Pipette

Understanding the components of a pipette is crucial for its effective use:

• Barrel: The main body that holds the liquid.
• Plunger: A movable part that creates suction to draw liquid into the barrel.
• Tip: The narrow end through which liquid is dispensed.
• Volume Adjustment Mechanism: Allows users to set the desired volume to be aspirated or dispensed.
• Ejector Button: Used to remove disposable tips after use.

Types of Pipettes

1. Volumetric Pipettes:
   • Design: Features a single graduation mark for precise volume measurement.
   • Use Case: Ideal for preparing standard solutions and conducting titrations.
2. Graduated Pipettes:
   • Design: Multiple markings along the length allow for variable volume dispensing.
   • Use Case: Commonly used in routine laboratory work where precision is less critical.
3. Micropipettes:
   • Design: Used for measuring very small volumes (microliters).
   • Types: Fixed Volume Micropipette and Variable Volume Micropipette.
   • Use Case: Essential in molecular biology applications like PCR and ELISA.
4. Serological Pipettes:
   • Design: Graduated with a wide bore for transferring larger volumes.
   • Use Case: Commonly used in cell culture and media preparation.
5. Pasteur Pipettes:
   • Design: Simple glass or plastic tubes with a tapered end.
   • Use Case: Used for transferring small amounts of liquids without precision.
6. Electronic Pipettes:
   • Design: Automated pipetting devices that can aspirate and dispense liquids with minimal user intervention.
   • Use Case: Ideal for high-throughput applications where speed and accuracy are critical.
7. Positive Displacement Pipettes:
   • Design: Use a piston mechanism that comes into contact with the liquid.
   • Use Case: Best suited for viscous or volatile substances. Read more for types of pipettes.

Procedure for Using a Pipette

Using a pipette correctly is essential to ensure accuracy:

1. Preparation: Choose the appropriate type of pipette based on your needs (volume and liquid type). Attach a clean tip securely to the pipette.
2. Setting Volume: Adjust the volume setting using the volume adjustment mechanism until it clicks into place.
3. Aspirating Liquid: Press the plunger to the first stop. Immerse the tip into the liquid without touching the bottom of the container. Slowly release the plunger to draw up the liquid into the tip.
4. Dispensing Liquid: Position the tip over the receiving container. Press down on the plunger to dispense; press to the second stop if necessary to expel any residual liquid.
5. Ejecting Tip: Use the ejector button to remove the tip without contamination.

Uses of Pipettes

Pipettes are versatile instruments used across various fields:

• Chemical Laboratories: For preparing solutions and conducting experiments requiring precise measurements.
• Biological Research: Essential in molecular biology techniques such as PCR, DNA sequencing, and enzyme assays.
• Clinical Laboratories: Used in blood sampling, serology tests, and other diagnostic procedures.
• Pharmaceuticals: Employed in drug formulation and quality control processes.
• Education: Commonly used in teaching laboratories to demonstrate principles of measurement and chemical reactions.

Examples of Applications

1. In chemical analysis, volumetric pipettes are used to prepare standard solutions that require high accuracy for titrations.
2. Micropipettes are vital in molecular biology labs where precise volumes are needed for reactions involving enzymes or nucleic acids.
3. Serological pipettes facilitate large-scale media preparation in cell culture experiments by allowing quick transfer of liquids.

Conclusion

Pipettes play an essential role in laboratory settings due to their precision and versatility in handling liquids. Understanding their principles, parts, types, procedures, and applications can significantly enhance laboratory efficiency and accuracy. Whether conducting routine analyses or complex research experiments, mastering pipetting techniques is crucial for any laboratory professional.

Reference sources:

1. Pipettes: Principle, Types, Quality, Calibration, Precautions - This article provides an overview of different types of pipettes, their design, and specific applications in laboratory settings. It discusses air displacement and positive displacement mechanisms extensively. Medicallabscientist.org.
2. Pipettes: Types, Parts, Application, Limitations, Examples - This resource covers the various types of pipettes, their parts, and practical applications in scientific research. It also highlights the limitations and best practices for using pipettes effectively. Scienceinfo.com.
3. Pipette Basics: An Overview of Pipettes and Their Functionality - This blog post discusses the essential functions of pipettes in laboratory environments and provides insights into different types of pipettes and their specific use cases. Mason Technology.