Some colors absorb ultraviolet light

In absorption photometry, chemical reactions or the concentration of chemical compounds are recorded by measuring light or light absorption. It is therefore necessary to first work out some basics about light.


A solution has a certain color because it lets this color through, but absorbs the color that is complementary to this color.
Example: A solution appears red to our eyes because this solution absorbs the green light and transmits the complementary color red.

The following table shows the spectral colors of white light and the complementary colors.

redgreen490 - 580
blueyellow580 - 595
green Blueorange595 - 650
green (blue-green)red650 - 780

For example, in order to specifically measure the light absorption of a red solution, green light, i.e. light with a wavelength between 490 and 580 nm, must be sent through the cuvette.


In addition to visible light, UV light is also used in clinical chemistry for absorption photometric determinations.

UV light comprises electromagnetic radiation with wavelengths between 195 and 380 nm. It is very rich in energy and can lead to physical damage (e.g. sunburn).

Substances with isolated double bonds, triple bonds, peptide bonds and carbonyl groups as well as aromatic compounds absorb a lot of UV light. The most important molecule in clinical chemistry that is measured in the UV range is the coenzyme NADH (nicotinamide dinucleotide).