Mohr Pipette
The Mohr Pipette is a high-precision laboratory instrument designed for accurate and controlled delivery of liquid volumes. Made from borosilicate glass 3.3, this pipette is calibrated “To Deliver” (TD, Ex) and features graduation markings that do not extend to the tip, allowing for partial volume measurements with reduced risk of contamination.
Ideal for titration and analytical tasks, the Mohr pipette is commonly used in pharmaceutical, chemical, educational, and environmental laboratories. It is autoclavable, durable, and conforms to ISO 835 and ASTM E1293 standards.
Introduction to Mohr Pipette
In scientific laboratories, precise liquid measurement is the backbone of accuracy and reliability. Among the many tools designed for this purpose, the Mohr Pipette stands out as a trusted instrument. Whether used in chemistry, biology, or pharmaceutical research, this pipette ensures scientists can measure and transfer solutions with high precision.
But what exactly is a Mohr Pipette, and why is it so widely used? Let’s explore its structure, working principle, applications, and how it compares to other pipettes.
What is a Mohr Pipette?
A Mohr Pipette is a type of graduated glass pipette used to measure and transfer specific volumes of liquid. Unlike volumetric pipettes, which are designed for a single fixed volume, Mohr Pipettes have multiple graduation marks along the tube, allowing flexibility in measurement.
Historical Background and Development
The Mohr Pipette is named after Karl Friedrich Mohr (1806–1879), a German chemist known for advancing volumetric analysis. His design revolutionized laboratory practices by allowing more versatile and precise liquid measurement than previous methods.
Importance in Analytical Chemistry and Biology
Today, Mohr Pipettes are widely used in titrations, standard solution preparation, and biological assays. Their adaptability makes them an indispensable tool in both educational and professional laboratories.
Structure and Design of Mohr Pipette
Key Components and Features
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Graduated Marks – The tube is marked with volume graduations, usually in milliliters.
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Narrow Tip – Ensures controlled release of liquids.
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Bulb and Stem – Provides capacity and stability during measurement.
Materials Used in Manufacturing
Traditionally made from borosilicate glass, modern Mohr Pipettes may also use durable plastics for classroom and routine use.
Different Sizes and Capacities
Mohr Pipettes typically range from 0.5 mL to 50 mL, making them suitable for a variety of laboratory applications.
Working Principle of Mohr Pipette
The operation of a Mohr Pipette relies on gravity and liquid flow control. When filled, the liquid is held in place due to surface tension and released gradually by adjusting pressure at the top. Proper use of the meniscus reading ensures accurate measurements.
Mohr Pipette vs. Other Pipettes
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Mohr Pipette vs. Volumetric Pipette: Mohr offers flexibility with multiple graduations, while volumetric provides higher precision for a single volume.
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Mohr Pipette vs. Serological Pipette: Unlike serological pipettes, Mohr Pipettes are not “blow-out” pipettes and require careful meniscus reading.
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Advantages: Flexible, reusable, and accurate for variable volumes.
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Limitations: Requires skill, slower to use, and less precise than volumetric pipettes.
Step-by-Step Guide: How to Use a Mohr Pipette
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Preparation Before Use – Clean pipette with distilled water and ensure no air bubbles.
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Filling and Reading Meniscus – Use a pipette filler, ensuring the bottom of the meniscus aligns with the desired graduation.
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Dispensing the Solution – Hold vertically, allow liquid to drain, and stop at the correct mark.
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Cleaning and Maintenance – Rinse with distilled water and store upright to prevent damage.
Applications of Mohr Pipette
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Laboratory Titrations: Essential in acid-base and redox reactions.
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Measuring Liquids in Biology Experiments: Used in enzyme activity and growth media preparation.
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Clinical and Pharmaceutical Labs: Helps in solution preparation and drug formulation.
Accuracy and Calibration Techniques
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Calibration: Performed by weighing water delivered and comparing it to expected values.
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Common Errors: Misreading the meniscus, incorrect angle, or temperature effects.
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Best Practices: Always calibrate periodically and use a consistent technique.
Safety Guidelines for Using Mohr Pipette
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Handle glass pipettes carefully to avoid breakage.
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Never pipette by mouth—always use a filler device.
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Prevent contamination by cleaning thoroughly before each use.
Modern Alternatives to Mohr Pipette
While Mohr Pipettes remain popular, micropipettes and digital pipetting systems now offer faster and more precise solutions in advanced research.
Choosing the Right Mohr Pipette
When selecting a Mohr Pipette, consider:
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Volume range required.
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Accuracy and calibration needs.
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Material (glass vs. plastic).
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Supplier reliability.
Conclusion
The Mohr Pipette remains a cornerstone of laboratory science, valued for its versatility, precision, and historical significance. While modern micropipettes may dominate high-tech labs, Mohr Pipettes still play an essential role in teaching and routine experiments.
For researchers, students, and educators alike, mastering the proper use of this timeless tool ensures accurate, reliable results in every experiment.
FAQs on Mohr Pipette
Q1. What is the primary use of a Mohr Pipette?
It’s mainly used for measuring and transferring variable liquid volumes in titrations and laboratory experiments.
Q2. Is a Mohr Pipette more accurate than a volumetric pipette?
No, volumetric pipettes are more precise for fixed volumes, while Mohr Pipettes are flexible but slightly less accurate.
Q3. Can Mohr Pipettes be used for viscous liquids?
They’re best suited for aqueous solutions; viscous liquids may reduce accuracy.
Q4. How should I read the meniscus in a Mohr Pipette?
Always align the bottom of the meniscus with the calibration mark at eye level.
Q5. Are Mohr Pipettes reusable?
Yes, with proper cleaning and care, glass Mohr Pipettes are reusable for years.
Q6. What’s the difference between Mohr and Serological Pipettes?
Mohr Pipettes measure liquid between graduations, while serological pipettes dispense the total volume including the tip.