colorimeters

A colorimeter is an analytical instrument used to quantify the color strength of a solution by measuring how much light at a selected wavelength is absorbed or transmitted. Color intensity is related to the concentration of a colored species in the solution, enabling rapid, relatively inexpensive determinations in chemistry, biology, environmental testing, and clinical analysis.

Most colorimeters consist of a light source, a wavelength selector such as a filter, a sample holder or cuvette, a photodetector, and a readout device. The sample is placed in the instrument, a chosen wavelength passes through the sample, and the detector measures the transmitted light. The result is typically reported as absorbance or percent transmittance. Calibration with standards and baseline correction are common to ensure accuracy.

The operating principle is often described by the Beer-Lambert law, which relates absorbance to concentration via A = εbc, where A is absorbance, ε is the molar absorptivity, b is the path length, and c is the concentration. Colorimetric assays use chemical reactions that produce a colored product, the intensity of which indicates the amount of the target analyte.

Variants include simple colorimeters and more advanced photometers, with single-beam or dual-beam designs. Pocket or portable models offer field use, while benchtop units provide greater stability and precision. Advantages include ease of use, speed, and low cost, but limitations include susceptibility to interferences from sample color, turbidity, and the accuracy generally being lower than that of full spectrophotometers.