Colorimeter in chemistry

A colorimeter is a device used in colorimetry. In scientific fields the word generally refers to the device that measures the absorbance of particular wavelengths of light by a specific solution.  This device is commonly used to determine the concentration of a known solute in a given solution by the application of the Beer-Lambert law, which states that the concentration of a solute is proportional to the absorbance.

Construction

The essential parts of a colorimeter are:

a light source (often an ordinary low-voltage filament lamp);

an adjustable aperture;

a set of colored filters;

a cuvette to hold the working solution;

a detector (usually a photoresistor) to measure the transmitted light;

a meter to display the output from the detector.

In addition, there may be:

a voltage regulator, to protect the instrument from fluctuations in mains voltage;

a second light path, cuvette and detector. This enables comparison between the working solution and a "blank", consisting of pure solvent, to improve accuracy.

There are many commercialized colorimeters as well as open source versions with construction documentation for education and for research.

Filters:- Changeable [Filter (optics)|optics filters]are used in the colorimeter to select the wavelength which the solute absorbs the most, in order to maximize accuracy. The usual wavelength range is from 400 to 700 [nanometer] (nm). If it is necessary to operate in the [ultraviolet]range then some modifications to the colorimeter are needed. In modern colorimeters the filament lamp and filters may be replaced by several (light-emitting diode)of different colors.The Measurement of Colour.

Cuvettes

Main article: Cuvette

In a manual colorimeter the cuvettes are inserted and removed by hand. An automated colorimeter (as used in an AutoAnalyzer) is fitted with a flowcell through which solution flows continuously.

Output

The output from a colorimeter may be displayed by an analogue or digital meter and may be shown as transmittance (a linear scale from 0-100%) or as absorbance (a logarithmic scale from zero to infinity). The useful range of the absorbance scale is from 0-2 but it is desirable to keep within the range 0-1 because, above 1, the results become unreliable due to scattering of light.

In addition, the output may be sent to a chart recorder, data logger, or computer.

Source From Wikipedia