Accurate sample preparation is crucial in various scientific and medical laboratories. Micropipettes, precision instruments designed to measure and transfer small volumes of liquid, are indispensable tools in achieving this. Here, we outline key techniques and best practices to ensure high accuracy and precision in micropipette usage.
Choosing the Right Micropipette
Selecting the appropriate micropipette for your task is the first step towards accurate sample preparation. Micropipettes come in different volume ranges:
- P2: 0.2 – 2 µL
- P10: 0.5 – 10 µL
- P20: 2 – 20 µL
- P200: 20 – 200 µL
- P1000: 100 – 1000 µL
Choose a micropipette that allows you to measure within 35-100% of its capacity to maximize accuracy and precision.
Proper Pipette Calibration
Regular calibration ensures the accuracy of micropipettes. Calibration involves adjusting the pipette to dispense the correct volume, typically performed by:
- Weighing dispensed water and comparing it to the expected volume.
- Adjusting the internal mechanisms if discrepancies are found.
Technique for High Accuracy
- Pre-wetting the Tip: Aspirate and dispense the liquid back into the source a few times before taking the final volume. This helps in equilibrating the temperature of the liquid and the tip.
- Angle and Immersion Depth:
- Hold the micropipette vertically.
- Immerse the tip slightly below the liquid surface (1-2 mm for small volumes and up to 6-10 mm for larger volumes).
- Smooth Operation:
- Press the plunger to the first stop before immersing the tip.
- Aspirate slowly and smoothly to avoid bubbles.
- Pause briefly after aspirating to allow the liquid to settle.
- Withdraw the tip from the liquid smoothly.
- Dispensing:
- Touch the tip against the side of the receiving vessel.
- Press the plunger to the first stop to dispense the liquid.
- After dispensing, press to the second stop to expel any remaining liquid.
- Consistent Speed and Pressure: Maintain consistent plunger pressure and speed during aspiration and dispensing to reduce variability.
Avoiding Common Errors
- Temperature Effects: Both the pipette and liquid should be at the same temperature to avoid volume discrepancies.
- Tip Attachment: Ensure the tip is securely attached to prevent air leakage.
- Pipette Position: Keep the pipette vertical during aspiration to avoid inconsistent volumes.
Regular Maintenance and Quality Control
- Clean the Pipette: Regularly clean the pipette, especially the piston and tip cone, to prevent contamination and ensure smooth operation.
- Routine Checks: Perform routine checks for leaks and calibration issues.
- Training and Practice: Ensure that all users are adequately trained and practice regularly to maintain skill levels.
Conclusion
Mastering micropipette techniques is essential for high-accuracy sample preparation in scientific research and diagnostics. By choosing the right micropipette, following precise techniques, and maintaining the instrument regularly, researchers can achieve reliable and reproducible results. Regular training and adherence to best practices further ensure the integrity of the sample preparation process.
Article by
Emmanuel Popoola
Emmanuel@aasnig.com