Pipette calibration ensures accurate and consistent liquid dispensing. It is typically performed gravimetrically by weighing dispensed distilled water and calculating the corresponding volume using environmental factors (Z-factor). The process involves pre-wetting the tip, taking multiple measurements, adjusting the pipette, and verifying against standards such as ISO 8655.
Gravimetric Pipette Calibration Steps
1. Gather Equipment
- Analytical balance (±0.0001 g or better)
- Distilled water (equilibrated to room temperature)
- Calibrated thermometer
- Barometer (optional)
- Pipette tips
- Beaker or container
2. Record Environmental Conditions
Note water temperature, atmospheric pressure, and humidity, and calculate the Z-factor for accurate volume conversion.
3. Pre-wet & Tare
Attach a pipette tip and aspirate/dispense water at least three times. Tare the balance with an empty vessel.
4. Weigh Dispensed Water
Aspirate the set volume, dispense into the vessel, and record the weight. Repeat approximately 10 times to ensure consistency.
5. Calculate Volume
Use the formula: V = w × Z, where w is the measured weight and Z is the conversion factor.
6. Adjust (if Needed)
Use the calibration key or screw: turn clockwise to increase volume, counter-clockwise to decrease.
7. Verify & Record
Repeat measurements until the pipette delivers the correct volume. Apply a calibration sticker with the date to indicate successful calibration.
Frequency
Pipettes should be calibrated every 3–6 months, or according to your laboratory protocols.
