Pipetting may seem simple, but precision begins with technique. One of the most overlooked factors affecting both accuracy and precision is how deeply you immerse the pipette tip into the liquid during aspiration. Too deep or too shallow—both can cause volume errors that compromise your results.
Understanding and consistently applying the correct immersion depth is critical, especially when working with small volumes or sensitive assays.
Recommended Tip Immersion Depths
Immersion depth should be adjusted based on the pipette’s volume range. Below are general guidelines:
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1–100 μL: 1–2 mm below the liquid surface
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100–1000 μL (1 mL): 2–4 mm (up to 6 mm if needed)
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Above 1 mL: 6 mm or more
Note: Depth is measured from the liquid surface, not the container’s bottom. Contact with the container base or wall can introduce surface tension effects and lead to volume inconsistencies.
Best Practices for Proper Aspiration
To ensure accurate pipetting, follow these key operational tips:
1. Keep It Vertical
Hold the pipette within ±20° of vertical to maintain uniform pressure and avoid drawing excess liquid.
2. Avoid Touching the Container
Don’t let the tip touch the bottom or sides of the container—this can disturb the liquid surface and affect volume uptake.
3. Aspirate Slowly and Steadily
Release the plunger gently—especially with higher volumes—to prevent bubbles and under-aspiration. Take about 1–2 seconds for a smooth draw.
4. Pre-wet the Tip
Pre-wet by aspirating and dispensing the sample liquid 1–3 times. This conditions the tip wall and improves reproducibility.
5. Pause Before Withdrawal
After releasing the plunger, wait 1–2 seconds before removing the tip from the liquid to allow full uptake.
6. Remove Excess Drops
Lightly touch the tip to the container’s inner edge when exiting to eliminate droplets on the outer tip wall.
Exceptions to the Rule
Certain sample types and volumes call for adjusted handling:
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Viscous Samples (e.g., glycerol): Use a slightly deeper immersion and aspirate slowly to ensure complete uptake.
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Volatile Liquids (e.g., ethanol): Minimize wait time post-aspiration and use pre-wet tips to reduce evaporation errors.
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Ultra-Low Volumes (<1 μL): Stick to ~1 mm or less to avoid overdraw due to capillary action.
Final Thoughts
Pipetting accuracy isn’t just about the instrument—it’s also about technique. Tip immersion depth might seem like a small detail, but it can make a big difference in experimental consistency and data quality.
Mastering this simple habit is one of the easiest and most impactful ways to improve your pipetting precision—no calibration required.