Beer-Lambert Law: A Fundamental Principle in Spectrophotometry
Introduction
The Beer-Lambert law is a fundamental principle in spectrophotometry, which is a technique used to analyze the concentration of substances in a solution based on their absorption of light. It relates the attenuation of light passing through a sample to the properties of the material, including its concentration and path length.
Historical Development
Bouguer's Law
In 1729, Pierre Bouguer established that the absorption of light by a material is proportional to the thickness of the material, which is known as Bouguer's law.
Beer's Law
In 1852, August Beer further developed Bouguer's findings and proposed that the absorbance of light by a solution is directly proportional to the concentration of the absorbing species. This relationship is known as Beer's law.
Combined Beer-Lambert Law
In 1905, Lambert combined Bouguer's and Beer's laws, resulting in the modern formulation of the Beer-Lambert law, which encompasses both the effects of path length and concentration on the attenuation of light.
Mathematical Formulation
The Beer-Lambert law equation is given by:
A = εbc
where:
- A is the absorbance, a measure of the attenuation of light
- ε is the molar absorptivity, a constant that depends on the absorbing species and the wavelength of light
- b is the path length, the distance the light travels through the sample
- c is the concentration of the absorbing species
Applications
The Beer-Lambert law is widely used in various fields, including:
- Analytical chemistry: Determining the concentration of substances in solutions
- Biochemistry: Studying protein and DNA concentrations
- Environmental monitoring: Measuring pollutants and contaminants
- Medicine: Analyzing bodily fluids and detecting diseases
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