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Accuracy and precision are fundamental in laboratory work. Experimental results may lose validity if instruments are not properly adjusted. Among the most widely used tools in chemistry, biology, and health sciences, the pipette is indispensable since it allows transferring very specific liquid volumes. However, to ensure reliable results, regular calibration is required. This article explains what pipette calibration means, the available methods, practical steps, and essential recommendations to perform it correctly.
What Does Calibrating a Micropipette Mean?
micropipette calibration consists of comparing the dispensed volume with a standard or reference value. This process ensures the pipette measures as close as possible to the manufacturer’s specification. The goal is to minimize systematic errors and maintain accuracy in experimental work. It is important to distinguish between calibration (verification), adjustment (correction of deviations), and maintenance (preventive actions such as cleaning and lubrication).
Micropipette Calibration Methods
Several methods can be used to calibrate pipettes:
- Gravimetric method: the most widely used and recommended by ISO 8655. It consists of weighing distilled water dispensed by the pipette and converting the mass into volume using water density at ambient temperature.
- Photometric or colorimetric method: mainly applied to micropipettes with small volumes, based on measuring the absorbance of a standardized colored solution.
- Alternative methods: some labs use automated systems to simplify calibration, though these are less common.
Each method has advantages and limitations, but the gravimetric approach is the most widespread due to its precision and ease of use.
Steps to Calibrate Micropipettes Correctly
Calibration should follow these steps:
1. Preparation: control temperature and humidity and use a calibrated balance.
2. Volume selection: choose at least three representative volumes (maximum, medium, minimum).
3. Dispensing and weighing: dispense distilled water into a pre-weighed container and record the mass.
4. Recording results: perform at least 10 repetitions per selected volume.
5. Calculation of accuracy and precision: convert the mass into volume and compare with reference values.
6. Interpretation and adjustment: determine if the results are acceptable or if adjustment is required.
7. Documentation: record the entire process to ensure laboratory traceability.
Recommendations and Best Practices in Micropipette Calibration
- Keep pipettes clean and in good condition.
- Follow the calibration frequency set by internal procedures or regulations.
- Avoid sudden temperature changes before use.
- Operate pipettes vertically and with the correct technique.
- Document every calibration and archive results to comply with audit requirements.
Advantages of Regular Calibration and Risks of Not Doing It
Advantages:
- Ensures reproducible and reliable results.
- Complies with regulations and external audits.
- Reduces experimental errors and saves resources.
Risks:
- Invalid data.
- Loss of valuable reagents and samples.
- Non-compliance in inspections or certifications.
Frequently Asked Questions
How often should micropipettes be calibrated?
Pipettes should be calibrated every 3–6 months, although frequency may vary depending on usage and laboratory policies.
Can pipettes be calibrated in the laboratory or is an external service required?
Calibration can be done in-house if the lab has the proper equipment and expertise, though many institutions use accredited external services.
What international standards regulate pipette calibration?
ISO 8655 is the most widely recognized international standard, though some industries have specific regulations.
How do I know if a pipette needs adjustment in addition to calibration?
If calibration results show deviations outside acceptable ranges, additional adjustment by trained staff or the manufacturer is required.
