Beer-Lambert Law

The Beer-Lambert law relates the attenuation of light to the material’s properties through which the light travels. Beer-Lambert law is applied to chemical analysis measurements. Let us familiarise ourselves with the law by reading the article.

What is the Beer-Lambert Law?

Beer’s law states the following:

For a given material, the sample path length and concentration of the sample are directly proportional to the absorbance of the light.

Various Names for Beer-Lambert Law

The Beer-Lambert law, known by various names such as the Lambert-Beer law, Beer-Lambert–Bouguer law or the Beer’s law. The Beer-Lambert law is known by so many names because more than one law is involved.

• In 1729, Pierre Bouguer discovered the law.
• Later, in 1760, Johann Heinrich Lambert quoted Bouger’s discovery saying that the absorbance of a sample is directly proportional to the path length of light. Although Lambert dint claim the discovery, he was often credited with it.
• In 1852, August Beer discovered a related law which stated that the absorbance is proportional to the concentration of the sample.

Beer-Lambert Law Equation

Where,

I is the intensity

I₀ is the initial intensity

μ is the coefficient of absorption

x is the depth in metrer

Beer-Lambert Law Applications

This law finds applications in various fields such as:

Analytical chemistry

This analysis mainly concentrates on the separation, quantification, and identification of matter by spectrophotometry. There is no involvement of extensive pre-processing of the sample to get the results. For example, bilirubin count in a blood sample can be determined by using a spectrophotometer.

In atmosphere

Solar or stellar radiation in the atmosphere can be described using this law. The law in atmospheric applications has a modified

Where,

a is the aerosols

g is the mixed gases

RS is the Raman scattering effect.

NO₂ is Nitrogen dioxide

w is the water vapour absorption

O₃ is Ozone

r is Rayleigh scattering

Beer-Lambert Law Limitations

Using this law it becomes easy to study the absorptivity coefficient of the sample when the concentration is low i.e. <10mM but as the concentration becomes high i.e. >10mM there is a deviation as the electrostatic interactions become more.