Colorimetric analysis

Colorimetric analysis is a method of determining the concentration of a chemical element or chemical compound in a solution with the aid of a color reagent. It is applicable to both organic compounds and inorganic compounds and may be used with or without an enzymatic stage. The method is widely used in medical laboratories and for industrial purposes, e.g. the analysis of water samples in connection with industrial water treatment.

The equipment required is a colorimeter, some cuvettes and a suitable color reagent. The process may be automated, e.g. by the use of an AutoAnalyzer or by Flow injection analysis. Recently, colorimetric analyses developed for colorimeters have been adapted for use with plate readers to speed up analysis and reduce the waste stream.

Calcium + o-cresolphthalein complexone ----> colored complex

Copper + bathocuproin disulfonate ----> colored complex

Creatinine + picrate ----> colored complex

Iron + bathophenanthroline disulfonate ---> colored complex

Phosphate + ammonium molybdate + ammonium metavanadate ----> colored complex

In enzymatic analysis (which is widely used in medical laboratories) the color reaction is preceded by a reaction catalyzed by an enzyme. As the enzyme is specific to a particular substrate, more accurate results can be obtained. Enzymatic analysis is always carried out in a buffer solution at a specified temperature (usually 37°C) to provide the optimum conditions for the enzymes to act. Examples follow.

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