LambertBeer

The Lambert-Beer Law, also known as Beer-Lambert Law or simply Beer's Law, is a fundamental principle in spectroscopy that describes the attenuation of light as it passes through a material. The law quantifies how much light is absorbed by a sample based on its concentration and the path length of the light through the sample. It is widely used in analytical chemistry for determining the concentration of substances in solution.

The law is mathematically expressed as A = εcl, where:

- A is the absorbance of the sample,

- ε (epsilon) is the molar absorptivity (or extinction coefficient) of the substance,

- c is the concentration of the substance in mol/L,

- l is the path length of the light through the sample in centimeters.

The relationship assumes that the absorbing species is homogeneously distributed, the incident light is monochromatic, and the sample is dilute enough that it does not scatter light significantly. Deviations from these conditions can lead to inaccuracies in measurements.

The Lambert-Beer Law was developed independently by Johann Heinrich Lambert (1728–1777) and Pierre Bouguer (1698–1758) in the 18th century, with later refinements by Johann Heinrich Poggendorff (1796–1877) and August Beer (1805–1863). While Lambert originally studied light transmission through gases, Beer later expanded the principle to apply to solutions.

This law is essential in techniques such as ultraviolet-visible (UV-Vis) spectroscopy, where it allows chemists to measure the concentration of colored or transparent substances by observing how much light they absorb at specific wavelengths. It is also foundational in other spectroscopic methods, including infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy, though variations and corrections may apply depending on the technique.