Normalization (Overview)

In the linear range, the response (either absorbance or current) recorded at a particular retention time is always proportional to the concentration of the substance currently in the flow cell. An objective comparison of two responses is therefore only possible if the concentration is identical.

As this condition is rarely achieved, and as it is not possible to convert a response recorded at a specific concentration to another concentration, the height of one response must be scaled to the height of the other. This is called normalization. The following factors must be considered:

• The base area portion must be considered - especially in trace analysis (see Baseline Correction of Spectra).

• In UV detection, the noise portion depends on the wavelength and the solvent. Thus, at 200nm, not only is the lamp energy of a deuterium lamp considerably lower than at 250nm, but the absorption of common solvents is also especially high.

• In amperometric detection, the noise intensity depends on the value of the applied potential. The higher the applied potential the higher the noise tends to be.

• Normalization should be performed where little influence on the above factors is expected and where a relative response maximum of the substances to be compared is observed.

Therefore, normalization can be performed by the Absolute Maximum, by the Relative Maximum, by a fixed Wavelength (for UV spectra), or by a Fixed Time (for I-t plots).

 Note:

Chromatograms and peaks can also be compared. They are referred to as normalized chromatograms, areas, or amounts.