A colorimeter is a device used in the practice of colorimetery, or the science of colour. Colorimetry has also been termed the quantitative study of colour perception. A number of instruments are available to determine the concentration of a solution. The simplest of those instruments is a colorimeter.
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A colorimeter is a device used to measure the absorption of a specific wavelength of light by a solution, which can in turn be used to determine the concentration of a solute in a solution.
The critical parts of a colorimeter are a light source (commonly a low-voltage filament lamp), adjustable aperture, coloured filters, solution cuvette, a transmitted light detector (such as a photoresistor) and an output display meter. Some colorimeters might also contain a regulator to prevent damage related to the machine from voltage fluctuations as well as a second light path to allow comparison between two solutions.
A filter is used to select and measure the wavelength of light that the solution absorbs the most. The measurements are done in nanometres (nm). Typically, the wavelength used is between 400nm and 700nm.
Following the reading, the colorimeter will provide data in either an analogue or digital formation, depending upon the machine. The data can be shown as transmittance on a linear percentage scale between 0 per cent and 100 per cent. It can also be shown as absorbance on a logarithmic scale between zero and infinity. Typically, the range of absorbance is from 0 to 2 with the ideal range being between 0 to 1.
The colorimeter was invented by Jan Szczepanik and applies the Beer-Lambert law when determining the concentration. The Beer-Lambert law states that absorbance is proportional to the concentration of a solute.