Introduction
Graduated pipettes are indispensable tools in laboratories worldwide, essential for precise measurement and transfer of liquids. Whether you’re working in chemistry, biology, or medical labs, understanding the nuances of graduated pipettes is critical for ensuring accuracy and efficiency in your experiments. This guide provides a thorough overview of graduated pipettes, including their types, features, differences from other pipettes, and practical tips for proper use.
1. What is a Graduated Pipette?
A graduated pipette is a glass or plastic tube marked with a series of lines (graduations) to measure specific volumes of liquid. Unlike volumetric pipettes, which measure a single, fixed volume, graduated pipettes allow users to measure varying volumes, making them versatile for different applications.
Types of Graduated Pipettes
- Mohr Pipette (Subterminal Pipette):
- Graduation: Stops before the tip.
- Usage: Commonly used in titrations where precise volume control is needed.
- Serological Pipette (Terminal Pipette):
- Graduation: Extends to the tip.
- Usage: Ideal for transferring liquids where the entire contents need to be dispensed.

2. Key Features of Graduated Pipettes
- Material: Available in glass (borosilicate) or plastic, each offering distinct benefits in terms of chemical resistance and durability.
- Calibration: Graduated pipettes are often calibrated to deliver (TD) or to contain (TC) specific volumes.
- Size Variations: Available in multiple sizes, from 0.1 mL to 25 mL, with 1 mL, 5 mL, and 10 mL being the most commonly used in laboratories.
- Accuracy: Smaller pipettes provide higher accuracy, making them ideal for critical measurements.
3. Differences Between Graduated Pipettes and Other Laboratory Tools
- Volumetric Pipettes:
- Purpose: Designed for measuring a single, exact volume with high accuracy.
- Comparison: While volumetric pipettes offer higher precision, graduated pipettes provide flexibility in measuring different volumes.
- Burettes:
- Purpose: Used primarily in titration to dispense known quantities of a liquid reagent.
- Comparison: Unlike graduated pipettes, burettes are equipped with a stopcock for controlled liquid release.
4. How to Use a Graduated Pipette Correctly
Using a graduated pipette accurately requires practice and precision:
- Filling the Pipette: Hold the pipette by the upper third and use a suction device to draw liquid above the desired graduation mark.
- Meniscus Reading: Ensure the meniscus (the curved surface of the liquid) aligns with the graduation mark when viewing at eye level.
- Dispensing Liquid: Gently release the liquid into the desired container, stopping when the meniscus reaches the target volume.
Tip: Always pre-wet the pipette with the liquid you will be measuring to ensure accuracy and reduce errors caused by surface tension.
5. Common Applications of Graduated Pipettes
Graduated pipettes are widely used in:
- Chemistry Labs: For preparing solutions of precise concentrations.
- Biology Labs: For cell culture work and media preparation.
- Medical Testing: In procedures requiring the measurement and transfer of biological fluids.
6. Maintaining and Calibrating Graduated Pipettes
Proper maintenance and calibration are crucial for the longevity and accuracy of your graduated pipettes:
- Cleaning: Rinse with distilled water after each use to prevent residue build-up.
- read more:How to clean glassware in laboratory
- Calibration: Regular calibration is necessary, especially if the pipette is frequently used. This ensures continued accuracy in measurements.
Conclusion
Graduated pipettes are versatile and essential tools in any laboratory setting, offering flexibility and precision for various liquid measurement tasks. Understanding their types, features, and proper usage can significantly enhance the accuracy of your experimental results.
External Resources:
- American Chemical Society on Pipettes
- ISO Standards for Laboratory Glassware
- National Institute of Standards and Technology (NIST) on Calibration
By following these guidelines and ensuring regular maintenance, you can make the most out of your graduated pipettes and achieve precise results in your laboratory work.