Micropipette: Types, Parts, Principle, and Uses in Laboratory Applications

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Micropipette: Types, Parts, Principle, and Uses in Laboratory Applications

Micropipettes are precision laboratory instruments used to measure and transfer very small volumes of liquid, typically in microliters (µL). They are essential tools in microbiology, pharmaceutical, chemical, and molecular biology laboratories where accuracy and precision are critical. This article provides a detailed explanation of the micropipette’s types, parts, principle, working mechanism, and applications.

What Is a Micropipette?

A micropipette is a laboratory instrument designed to measure and transfer small, precise volumes of liquids ranging from 0.1 µL to 1000 µL. It operates on the air displacement principle, using a piston to create a vacuum and dispense liquid accurately. Micropipettes are indispensable in analytical and biological laboratories for activities like solution preparation, sample dilution, and reagent addition.

Principle of Micropipette

The working of a micropipette is based on the air displacement principle. When the plunger is pressed, a piston moves downward, pushing out air from the pipette tip. Upon releasing the plunger, the piston moves upward, creating a partial vacuum that draws liquid into the tip. When pressed again, the liquid is expelled precisely, ensuring accurate volume transfer.

Some specialized micropipettes (like positive displacement pipettes) work on the positive displacement principle, where a disposable piston directly contacts the liquid, preventing air interference — ideal for viscous or volatile samples.

Parts of a Micropipette

A micropipette consists of several mechanical and functional parts that ensure accuracy, precision, and ease of use. The major parts include:

  • Plunger Button: Used to aspirate and dispense liquid; operates in two stages – aspiration and delivery.
  • Tip Ejector Button: Used to remove disposable pipette tips after use without manual contact.
  • Volume Adjustment Knob: Allows users to set the desired volume by rotating clockwise or counterclockwise.
  • Volume Display: A digital or mechanical readout showing the set volume in microliters (µL).
  • Shaft or Barrel: The main body connecting the plunger mechanism and the tip cone.
  • Tip Cone: The lower end of the pipette where disposable tips are fitted.
  • Piston and Spring Assembly: Responsible for air displacement and volume control.
  • Disposable Tip: A plastic tip used for liquid aspiration and dispensing, ensuring no contamination.

Types of Micropipettes

Micropipettes are classified based on their mechanism, design, and volume range:

1. Based on Volume Adjustment

  • Fixed Volume Micropipette: Delivers a constant pre-set volume. Used where repeated, identical volume transfers are required.
  • Variable Volume Micropipette: Allows users to adjust the volume within a specific range (e.g., 10–100 µL).

2. Based on Operation Principle

  • Air Displacement Micropipette: Uses an air cushion between the piston and liquid. Most common in labs for aqueous samples.
  • Positive Displacement Micropipette: Contains a disposable piston that comes into contact with the sample. Ideal for viscous or volatile liquids.

3. Based on Channel Design

  • Single-Channel Micropipette: Used for transferring one sample at a time.
  • Multi-Channel Micropipette: Commonly used in ELISA and microplate assays (8 or 12 channels).
  • Electronic Micropipette: Motorized pipettes providing high accuracy and user comfort.

Working Mechanism of a Micropipette

  1. Attach a sterile, compatible pipette tip to the shaft.
  2. Set the required volume using the adjustment knob.
  3. Press the plunger to the first stop and immerse the tip into the liquid.
  4. Release the plunger slowly to aspirate the desired volume.
  5. Dispense the liquid by pressing the plunger to the second stop.
  6. Eject the tip using the tip ejector button to prevent contamination.

Note: Always hold the pipette vertically while aspirating and at a slight angle while dispensing to maintain accuracy.

Calibration of Micropipette (Brief Overview)

To ensure accuracy and precision, micropipettes must be regularly calibrated using the gravimetric method — measuring the weight of water and converting it to volume. Calibration confirms that the micropipette dispenses the correct volume within specified tolerance limits as per ISO 8655 standards.

Uses of Micropipette in Laboratory Applications

Micropipettes are extensively used across various scientific disciplines. Some of the key applications include:

  • Microbiology: For transferring inoculums, diluting cultures, and preparing media.
  • Pharmaceutical Analysis: Used in sample preparation, assay testing, and quality control.
  • Molecular Biology: For DNA extraction, PCR setup, and gel electrophoresis sample loading.
  • Biochemistry: Enzyme assays, reagent addition, and buffer preparation.
  • Clinical Laboratories: Sample dilution, reagent dispensing, and diagnostic testing.
  • Chemical Laboratories: Standard solution preparation and titration studies.

Best Practices for Using Micropipettes

  • Pre-wet the pipette tip before actual use to improve accuracy.
  • Always use high-quality, manufacturer-recommended tips.
  • Store the pipette vertically after use to avoid liquid damage.
  • Avoid laying the pipette horizontally with liquid inside.
  • Calibrate and maintain micropipettes regularly.
  • Handle gently to prevent internal piston damage.

Common Errors in Micropipette Use

  • Air bubbles in tips leading to inaccurate aspiration.
  • Using damaged or incompatible tips.
  • Incorrect pipetting angle or speed.
  • Temperature variations affecting volume accuracy.
  • Not performing regular calibration or maintenance.

Advantages of Using Micropipettes

  • High accuracy and precision in liquid measurement.
  • Time-saving and easy to operate.
  • Prevents contamination with disposable tips.
  • Suitable for a wide range of volumes and sample types.

Conclusion

Micropipettes are vital tools for modern laboratories, offering precision and reliability in liquid handling. Understanding their types, parts, and working principles helps ensure accurate results and prevents measurement errors. Regular maintenance, calibration, and correct handling techniques are key to maintaining micropipette performance and laboratory data integrity.

References

  • ISO 8655 – Piston-operated volumetric apparatus
  • WHO Laboratory Quality Management System Handbook
  • Eppendorf and Gilson Micropipette Manuals
  • Pharmaceutical Microbiology Guidelines

💬 About the Author

Siva Sankar is a Pharmaceutical Microbiology Consultant and Auditor with extensive experience in sterility testing, validation, and GMP compliance. He provides consultancy, training, and documentation services for pharmaceutical microbiology and cleanroom practices.

📧 Contact: siva17092@gmail.com
📱 Mobile: 09505626106

Disclaimer: This article is for educational purposes and does not replace your laboratory’s SOPs or regulatory guidance. Always follow validated methods and manufacturer instructions.

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