Notes on Pipettes in the Laboratory

Medical Laboratory Assistant/Technician Program

Course Overview

• This program focuses on the crucial role of pipettes in clinical laboratories, which are essential tools for accurately measuring and transferring liquids.

• Emphasizes various aspects of pipetting, including safety protocols, classification, types, and proper maintenance of pipettes to ensure accuracy and reliability in laboratory results.

Course Objectives

• Identify and describe the various types of pipettes used in clinical laboratories, including their specific applications and operational principles.

• Discuss the importance of regular pipette maintenance and calibration, ensuring precision and reliability in laboratory results.

• Demonstrate how to correctly use both manual and automated pipettes in various laboratory settings.

• Understand the appropriate practices for disposing of pipette tips, reducing contamination risks.

• Learn the effective cleaning methods for reusable pipettes and bulbs to maintain laboratory hygiene and integrity.

Pipette Safety

• Use the pipette that is appropriate for the specific task to prevent contamination and deliver accurate results.

• Pipetting technique should be precise: Minimize pressure applied while pipetting.

  • Hold the pipette with a relaxed grip to reduce fatigue and improve control.

  • Maintain an ergonomic setup by ensuring comfortable seating positions and easy access to all laboratory supplies, which reduces strain during operations.

  • Eject pipette tips carefully to prevent aerosol formation, which can lead to contamination and exposure to hazardous materials.

  • Organize your workspace effectively by keeping clean pipettes to the left and used (dirty) ones to the right, thereby minimizing the risk of cross-contamination.

  • NEVER use mouth pipetting; always use a pipette bulb or other safe vacuum mechanism instead, to avoid inhaling hazardous substances.

Classification of Pipettes

• To Contain (TC): Pipettes designed to hold a defined volume of liquid but require rinsing to ensure complete transfer of the contents. Commonly used in applications where precise volume measurement is crucial.

• To Deliver (TD): Designed to deliver a defined volume of liquid and allow the liquid to drain by gravity; it is critical to blow out the last drop using a rubber bulb or an etch ring to ensure the exact volume is dispensed.

Classes of Pipettes

• Class A: Pipettes that are accurate to +/- 0.020 mL; manufactured to meet precise tolerances and standards required for quantitative analysis in laboratory settings.

• Class B: Allow for twice the error limits of Class A pipettes, making them suitable for less critical applications; the class is indicated on the pipette for clear identification.

Types of Pipettes

1. Glass or Plastic: Glass pipettes are reusable and more chemically resistant, while plastic pipettes are disposable, reducing the risk of contamination between experiments.

2. Volumetric Pipettes: These are precisely calibrated to deliver fixed volumes of liquid through drainage. Common materials include Pyrex or Kimax. These pipettes hold 1 mL or more and typically require a rubber bulb for effective use.

3. Graduated Pipettes (Mohr and Serological):

   • Mohr Pipettes: Feature calibration marks above the tip, suitable for non-critical measurements where precision is less of an issue.

   • Serological Pipettes: Calibration marks extend to the tip; the last drop must be blown out to ensure complete delivery, and they are calibrated for specific temperatures to accommodate liquid expansion and contraction.

4. Micropipettes: Designed for precise, rapid measurements and are piston-operated with capabilities for both single-channel and multi-channel systems. These pipettes typically come in both fixed and variable volume formats, suitable for various laboratory applications.

5. Transfer and Pasteur Pipettes: Disposable and designed for transferring liquids; not suitable for precise volume measurements but invaluable for general liquid handling tasks.

6. Capillary Tubes: Operate by capillary action to draw fluid; frequently utilized in specialized applications, such as blood films for hematological studies.

Micropipette Details

• Calibration: Should be conducted annually to maintain accuracy, with most manufacturers offering services for cleaning and calibration.

• Parts: Comprised of a tip ejector, plunger, volume adjuster, display, body, and head, each contributing to the overall functionality and ease of use.

• Volume Ranges: Available in ranges from 0.1 µl to 10 ml, accommodating a wide variety of laboratory tasks with differing tip sizes to suit the specific requirements of the experiment.

Pipette Tips Management

• Tip Removal: If a tip ejector is unavailable, you can use a tissue to remove the tip carefully. Always dispose of used tips without glove contact to maintain cleanliness.

• Micropipettes: Available in both fixed and variable volumes; fixed are known for their durability and accuracy, making them ideal for repetitive tasks, whereas variable volume allows flexibility for different experimental needs.

Cleaning and Maintenance

• Cleaning Procedure for Bulbs: Disassemble the bulb from its adapter; rinse thoroughly with deionized water and ensure it is completely dried to avoid contamination of future samples.

• Soaking and Cleaning Pipettes: Immerse pipettes in a cleaning solution for a minimum of 30 minutes, followed by rinsing under tap water for 1-2 hours and a final rinse with distilled water. Dry in a hot oven at 90°C for at least one hour to ensure all residues are removed.

Questions for Review

1. Compare and contrast TD vs TC pipettes in terms of usage and precision.

2. Differentiate between graduated and single volume pipettes, highlighting their specific applications.

3. Explain the difference between blowout and non-blowout pipette markings and their relevance in laboratory settings.

4. List various types of pipettes, their key features, and recommend situations for their optimal usage.