What are the two calibration methods for micropipettors?

• A. Gravimetric and Spectrophotometric
• B. Gravimetric and Calorimetric
• C. Gravimetric and Mechanical
• D. Spectrophotometric and Calorimetric

Answer: (A)

Calibration of micropipettors hinges on verifying that the volume set on the instrument is the volume actually delivered. One approach is gravimetric: weigh the water that the pipette dispenses, then convert that mass to volume using the density of water at the measured temperature. This method rests on the direct relationship between mass and volume for liquids, and it’s highly traceable to SI units via the balance and density data. It’s widely used because it’s straightforward and provides a precise, physical measure of delivered volume, with corrections for temperature and buoyancy as needed.

The other method is spectrophotometric. Here, a dye solution is used, and the amount delivered by the pipette is inferred from the optical signal it produces. By measuring absorbance and comparing it to a calibration curve that links absorbance to known volumes or concentrations, you can determine the delivered volume. This method leverages Beer-Lambert law and is useful for rapid, non-destructive verification, especially when a precise balance isn’t available.

Together, gravimetric and spectrophotometric approaches provide two independent, quantitative ways to confirm that a micropipettor delivers the intended volume.