You have a valid calibration certificate.
The pipette passed inspection.
Everything looks compliant.
And yet… your pipetting results are still unstable.
If this sounds familiar, you’re not alone.
Calibration is essential — but it is not a guarantee of perfect liquid handling.
In many labs, accuracy problems persist even when calibration is up to date.
Why?
Because calibration verifies volume under controlled conditions.
Your daily experiments are rarely performed under those exact conditions.
Let’s look at three commonly overlooked causes.
1️⃣ Tip Issues: Compatibility and Sealing
Even a perfectly calibrated pipette cannot compensate for a poor tip seal.
Common issues include:
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Slight incompatibility between pipette and tip
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Incomplete seating of the tip
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Air leakage at the shaft connection
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Variability between tip lots
If the seal is not airtight, aspiration volume changes — even if calibration values are correct.
Low-volume work (1–10 µL) is especially sensitive to this.
If results fluctuate unexpectedly, check the tip fit before questioning the instrument.
2️⃣ Environmental Factors: Temperature Differences
Calibration is typically performed at controlled room temperature.
But real lab conditions vary.
Consider:
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Cold reagents taken directly from 4°C storage
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Air-conditioned rooms with uneven temperature zones
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Warm hands holding the pipette for extended periods
Air-displacement pipettes rely on an internal air cushion.
When temperature changes, air expands or contracts — affecting volume delivery.
For example:
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Cold liquid reduces aspirated volume.
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Warm air inside the pipette expands and alters dispensing.
These physical effects are subtle — but measurable.
Calibration cannot eliminate environmental impact.
3️⃣ Operator Technique Variability
Even experienced users introduce variation.
Common technique-related causes include:
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Aspirating too quickly
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Removing the tip immediately after aspiration
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Skipping pre-wetting
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Changing immersion depth
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Slight angle differences during aspiration
At higher volumes, these differences may not matter.
At lower volumes, they can significantly impact reproducibility.
Calibration verifies mechanical performance — not technique consistency.
When Should You Suspect the Pipette Itself?
After ruling out:
✔ Tip sealing
✔ Environmental effects
✔ Technique variation
If inconsistencies persist, then consider:
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Internal seal wear
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Mechanical fatigue
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Need for maintenance or repair
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End-of-life replacement
But replacing a pipette should not be the first reaction.
Troubleshooting should be systematic.
Calibration Is Necessary — But Not Sufficient
Think of calibration as a health check.
It confirms that the instrument performs correctly under defined conditions.
It does not guarantee:
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Perfect tip compatibility
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Ideal lab temperature
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Consistent user technique
Accurate pipetting depends on the entire system:
Pipette + Tip + Environment + Operator
Ignoring any one of these creates variability.
Final Thoughts
If your pipette is calibrated but results still vary, don’t assume the instrument is defective.
Instead, ask:
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Is the tip sealing properly?
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Are temperature differences affecting air displacement?
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Is technique consistent across users?
Precision in liquid handling is rarely about one single factor.
It’s about controlling the variables you can.
And often, the problem is smaller — and more fixable — than you think.