How to perform a calibration

Principle of internal calibration


In an internal calibration, a compound (called internal standard) will be added to each standard solution. In this way, the standard solutions contain the compounds to be dosed, at ascending concentrations, as well as an internal standard added at the same concentration at each calibration point. This internal standard is added to all test samples at the same concentration.

This calibration is thus more complicated to undertake than external calibration - in practice, an internal calibration is performed when the analytical method lacks repeatability or reproducibility. A typical example of application is gas chromatography, where the injected volumes are hard to reproduce.


Interactive diagram: principle of the internal calibration method
for a spectrophotometric measurement
Information pictogram
When analyzing complex mixtures by chromatography, it might be necessary to add several internal standards.
Attention pictogram
In chromatography: the internal standard must be separable from the compound to be determined.
Next page
Previous page