The main application purpose of photometry takes place when the concentration of sample solutions is to be determined. This method is based on the Lambert-Beer's law, which describes the relationship between the absorbance of the sample at a certain wavelength and the concentration thereof. The measurement of the concentration of dissolved substances is designed to be as quickly and relatively simple as possible.
The term of qualitative analysis is described as a so-called identity resolution. It is used less frequently and has a not quite as high significance as the quantitative analysis. Not many substances show characteristic absorption maxima and thus release information on their purity under certain conditions. As quick reference here is the analysis of DNA (deoxyribonucleic acid) or RNA (ribonucleic acid) - the photometry is used regularly for this purpose.