Colorimeter (chemistry)

A colorimeter is a device used in

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

(1) Wavelength selection, (2) Printer button, (3) Concentration factor adjustment, (4) UV mode selector (Deuterium lamp), (5) Readout, (6) Sample compartment, (7) Zero control (100% T), (8) Sensitivity switch, (9)ON/OFF switch^[3]

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
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.^[4]

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 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.

Cuvettes

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

linear scale from 0 to 100%) or as absorbance (a logarithmic scale

from zero to infinity). The useful range of the absorbance scale is from 0 to 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.

Notes

^ Nuffield Advanced Chemistry (2003)
^ Portable CCD LED Colorimeter Spectroradiometer For CCT, CRI, CQS Test
^ Colorimetry
^ [1] Anzalone GC, Glover AG, Pearce JM. Open-Source Colorimeter. Sensors (2013); 13(4):5338-5346

References

The Nuffield Foundation 2003. March 30, 2003. [2] Archived 4 December 2011 at the Wayback Machine
"Colour." Encyclopædia Britannica. Encyclopædia Britannica Online. Encyclopædia Britannica Inc. (2011) Accessed 17 November 2011. [3]
"Colorimetry" Encyclopædia Britannica. Encyclopædia Britannica Online. Encyclopædia Britannica Inc. (2011) 17 November 2011. [4]
Orion Colorimetry Theory. The Technical Edge. [5]

[1] Nuffield Advanced Chemistry (2003)

[2] Portable CCD LED Colorimeter Spectroradiometer For CCT, CRI, CQS Test

[3] Colorimetry

[4] [1] Anzalone GC, Glover AG, Pearce JM. Open-Source Colorimeter. Sensors (2013); 13(4):5338-5346

[3]

[4]