What is the typical concentration unit required for the Beer-Lambert Law?

The Beer-Lambert Law is fundamental in spectroscopy and relates the absorption of light to the properties of the material through which the light is traveling. Specifically, the law states that the absorbance of a solution is directly proportional to its concentration and the path length of the light through the solution.

In this context, the typical concentration unit required for the Beer-Lambert Law is mol/dm³, which is equivalent to molarity (M). This is because absorbance is typically calculated using the molar absorptivity (also known as molar extinction coefficient), which is expressed in L/(mol·cm). Therefore, using mol/dm³ for concentration allows for a direct and consistent application of the Beer-Lambert equation, ( A = \varepsilon c l ) where ( A ) is absorbance, ( \varepsilon ) is the molar absorptivity, ( c ) is the concentration in mol/dm³, and ( l ) is the path length in cm.

While other concentration units like g/L, ppm, and mg/mL are used in various contexts, they don't align as directly with the molar absorptivity constants that are typically provided for most substances in spectroscopic studies