Photometers

The photometer analyses the content of a certain element in an aqueous substance. The measurement is reported in mg/l (or ppm). Photometry refers to the set of techniques for measuring light intensity, which is based either on the absorption of radiation by the sample under examination (absorption photometry) or on the emission of light by the sample, suitably excited (emission photometry). Photometry is understood if, and only if, the relationship between colour and light is clear. Colours are light-dependent and what we see as colour is derived from the effect of light on an object. Substances may or may not absorb light, with a particular colour. If a substance to be analysed absorbs yellow light, a transmission of blue light, its complement, will occur. Such blue light is the actual light we will see. Photometry (or also Colorimetry), exploits this principle, i.e. the colour variation in the sample under analysis. This variation is directly related to the concentration of the substance being sought. A colorimetric analysis is based on the principle that many substances, when reacting with a chemical compound, produce a change in colour that is directly proportional to the concentration of the substance being measured. Each sample exposed to a beam of light causes part of the radiation to be absorbed by the substance itself. The difference between the two radiations is decisive for colourimetric analysis. The amount of radiation is determined by the Lambert-Beer Law.