Overview
This lecture covers the step-by-step procedure for accurate and precise pipetting, highlighting essential techniques and common sources of error.
Selecting and Setting Up the Pipette
- Choose a pipette whose volume range includes your desired amount (e.g., 20–200 microliters for 100 microliters).
- Adjust the pipette to display the exact volume needed before use.
- Attach an appropriate tip that fits securely on the pipette; color codes may help but check fit.
Aspirating Liquid
- Before inserting into liquid, press the plunger until you feel resistance (the first stop).
- Submerge the tip just below the liquid surface to avoid coating the outside of the tip.
- Slowly release the plunger to aspirate liquid, keeping the tip under the surface to prevent bubbles.
Dispensing Liquid
- Hold the receiving container at a 45-degree angle and keep the pipette vertical.
- Gently dispense the liquid against the side of the container wall to ensure full delivery.
- After reaching initial resistance, continue pressing to the second stop to expel any remaining liquid.
- Withdraw the pipette tip before releasing the plunger to avoid drawing liquid back up.
Common Errors and Accuracy Checks
- Leaky or poorly sealed tips can cause inaccurate volumes.
- Reusing pipette tips can reduce measurement accuracy.
- Not dispensing against the container wall may leave drops behind, causing errors.
- To check accuracy, dispense multiple drops of 100 μL water onto a scale; each should weigh about 100 mg.
Key Terms & Definitions
- Pipette — a laboratory instrument used to measure and transfer small volumes of liquid.
- Plunger — the pushable part of the pipette controlling liquid uptake and release.
- Aspirate — to draw liquid into the pipette tip.
- Dispense — to release liquid from the pipette into another container.
Action Items / Next Steps
- Practice pipetting by dispensing 100 μL drops on a scale to test your accuracy.
- Review pipette and tip compatibility before each use.