Standardization is a calibration conducted by using samples of known composition to create standard curves which are used to calculate the composition of an unknown sample. Analytical grade compounds frequently are sufficiently pure to prepare standards adequate for the calibration of instruments. For many analyses, 2 or 3 significant figures are adequate, and instruments easily provide that precision. Very high purity chemicals may not be needed for standardization.

Whatever the source of the standards, the procedure is basically the same. The analyst prepares several standards at different concentrations over the range of concentrations that may be present in the unknown samples. A plot of instrument response versus concentration of analyte, the substance whose concentration is being determined, is prepared. The instrument response from any sample can then be compared to the standards data to calculate the concentration of analyte. These curves are a calibration of the instrument response to the concentration of analyte. Any calibration is only useful for the range of concentrations of analyte actually tested.

Straight lines make for easy manual calculations. Many data sets are a better fit by more complex curves, however. With the computers handling the statistical analysis of data, fitting data to the best curve is as fast as fitting data to a straight line.

NIST (National Institute of Standards and Technology) distributes expensive standards for very careful calibrations.