Colorimetry (chemical method)
Under colorimetry means the concentration determination of a substance in a liquid phase, usually 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 measurement principle of a photometer. Colorimeter, for example, also allow the measurement of substances that do not follow the Beer-Lambert law, such as colloidal solutions and suspensions.
Here, either the color intensity of a sample measured directly by visual comparison (with colored substances ), or the substance, after conversion into a colored reaction product from a chemical reaction, measured using a suitable reference scale. When measuring the color density of the substance to be measured is directly determined by the comparison scale. For color uniformity corresponds to the concentration of the substance which is printed on the scale value or the corresponding value in a table.
The measurement of the concentration is often determined by an optical calorimeter. This allows the eyes to direct color comparison of the substance to be measured with a calibrated color scale. This scale, which is inserted into the colorimeter, can of gelatin filters, glass filters or simply consist only of a printed paper scale. The color scale is often interchangeably to measure in an optical colorimeter to various substances or concentration ranges. For several years, this type of determination of the concentration is increasingly performed by electronic devices. This will measure generally only the intensity of a colored light source and compare these ( electronic) with corresponding values of a comparison table.
In medicine, the hemoglobin content was formerly often determined in blood by a colorimetric method. It is still used today, especially in pediatrics in newborns.
Colorimetric measurements are often in the hobby and especially in " field trials " because of the low expense - for example in environmental protection, or on expeditions - conducted to determine the content of metal ions (iron, lead, copper, manganese, etc. ) in a sample to be determined. Also for the analytical determination of peroxides or ozone colorimetry is still frequently used.