Colorimetry
Under colorimetry refers to the concentration determination of a substance in a mostly liquid phase by a comparison measurement with a color scale, which in turn corresponds to a known concentration of the substance. The colorimetry must not be confused with the measuring principle of a photometer . Colorimeters allow e.g. B. also the measurement of substances that do not follow the Lambert-Beer law , such as colloidal solutions and suspensions .
Either (in the case of colored substances) the color intensity of a sample is measured directly by optical comparison, or the substance is measured after conversion into a colored reaction product by means of a chemical reaction using a suitable comparison scale. During the measurement, the color density of the substance to be measured is determined directly with the comparison scale. If the colors are the same, the concentration of the substance corresponds to the value printed on the scale or the corresponding value in a table.
The measurement of the concentration is often determined with the aid of an optical colorimeter . This allows a direct color comparison of the substance to be measured with a calibrated color scale. This scale, which is inserted into the colorimeter, can consist of gelatin filters, glass filters or simply a printed paper scale. The color scale is often interchangeable in an optical colorimeter in order to measure different substances or concentration ranges. For some years now, this type of concentration determination has also been increasingly carried out with electronic devices. These generally only measure the intensity of a colored light source and compare this (electronically) with corresponding values from a comparison table.
application
In the past, the hemoglobin content in the blood was often determined by a colorimetric method in medicine. Today it is mainly used in pediatrics for newborns.
Colorimetric measurements are often used in aquaristics and especially in "field trials" - e. B. in environmental protection , or on expeditions - carried out to determine the content of metal ions ( iron , lead , copper , manganese, etc.) in a sample. Colorimetry is also still frequently used for the analytical determination of peroxides or ozone .
Individual evidence
- ↑ Otto-Albrecht Neumüller (Ed.): Römpps Chemie-Lexikon. Volume 3: H-L. 8th revised and expanded edition. Franckh'sche Verlagshandlung, Stuttgart 1983, ISBN 3-440-04513-7 , pp. 2177-2178.