Lambert-Beer's Law

Lambert-Beer's Law

Lambert-Beer's Law, also known as Beer-Lambert Law or Beer's Law, is a fundamental principle in analytical chemistry that describes the relationship between the absorption of light by a substance and the concentration of that substance in a solution. It is named after two scientists, August Beer and Johann Lambert, who independently formulated the law in the 19th century.

The Lambert-Beer Law is typically expressed as:

A = ε * c * l

Where:

A is the absorbance of light by the substance in the solution.

ε (epsilon) is the molar absorptivity (also called molar extinction coefficient or molar absorptivity constant) of the substance. It is a constant that depends on both the substance being analyzed and the wavelength of light used for measurement. It has units of L·mol⁻¹·cm⁻¹.

c is the concentration of the substance in the solution, usually expressed in moles per liter (Molarity, M).

l is the path length of the cuvette or container through which the light passes, typically measured in centimeters (cm).

The Lambert-Beer Law states that the absorbance of a solution is directly proportional to the concentration of the absorbing species and the path length, while also being directly proportional to the molar absorptivity at a specific wavelength of light. This law is particularly useful in quantitative analysis, such as in spectrophotometry, where it is used to determine the concentration of a solute in a solution by measuring its absorbance at a specific wavelength.

The law assumes that the substance in question follows Beer's law, which means that the concentration is in a linear relationship with the absorbance. Deviations from Beer's law can occur at very high concentrations or if there are strong interactions between the solute molecules.

In practical applications, scientists use spectrophotometers to measure the absorbance of a sample at a specific wavelength, and by knowing the molar absorptivity constant and the path length, they can determine the concentration of the substance in the solution. This is widely used in various fields, including chemistry, biochemistry, environmental science, and pharmaceutical analysis.

Anjalee Mishra