Beer's law

Beer's Law, also known as Beer-Lambert Law or Beer-Lambert-Bouguer Law, is a fundamental principle in the field of spectrophotometry. It describes the relationship between the absorption of light by a substance and the properties of the substance, specifically its concentration and path length.

History

The law was named after the German mathematician and chemist August Beer and the French mathematician and astronomer Pierre Bouguer. Bouguer discovered the law in 1729, while Beer extended it in 1852.

Statement of the Law

Beer's Law states that the absorbance (A) of a solution is directly proportional to its concentration (c) and the path length (l). This relationship is expressed mathematically as:

A = εcl

where:

• A is the measured absorbance,
• ε is the molar absorptivity or extinction coefficient, a constant for each substance,
• c is the concentration of the substance, and
• l is the path length that the light travels through the substance.

Applications

Beer's Law is widely used in the fields of chemistry, physics, and earth science to quantify the concentration of a substance in a solution. It is commonly used in laboratory analyses and quality control in industries such as food and beverage, pharmaceutical, and environmental monitoring.

Limitations

While Beer's Law is widely applicable, it has its limitations. It assumes that the absorbing species are homogeneously distributed throughout the sample and that the light absorption occurs independently. These assumptions may not hold true for high concentrations and complex mixtures.

See Also

• Spectrophotometry
• Absorption spectroscopy
• Molar absorptivity