Spectrophotometry or photometry

In this physicochemical method of investigation, light of a certain wavelength is beamed into the solution of a substance. The light is absorbed either entirely or partially by the molecules of the substance. 

As a result of the absorption of the light, the intensity of the light beam directed into the solution (Iq) is reduced as it passes through the sample. The residual intensity still present on exit (I) is measured with a suita- 

The degree of light absorption in certain spectral regions permits conclusions to be drawn as to the chemical structure of the substances. 

If the chemical structure of the substances is known, the concentration in the solution concerned may be deduced. The following distinctions are made, according to the wavelength region in which the absorption spectrum is measured. 

In spectrophotometry in the narrower sense the monochromatic light beam of a discrete wavelength is filtered from a polychromatic light beam in an accessory unit (monochromator prism or grating). In addition, monochromatic light may also be produced and used for analytical measurements 

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