12.9 : 紫外可见光谱：朗伯比尔定律

The Beer–Lambert law gives the relationship between absorbance, concentration, and path length of light through the sample.

The absorbance, A, of a solution, is the logarithmic function of the ratio of the intensity of the incident light, I₀, to the intensity of the transmitted light, I.

The absorbance also relies on molar absorptivity, ε, which is the absorbance of a 1 molar solution measured in a cell with a path length of 1 cm.

Absorptivity values above 10⁴,  are termed high-intensity absorptions, while those below 10³  are classified as low-intensity absorptions.

Molar absorptivity is a constant for a compound, and it is a characteristic of that compound at a particular wavelength. For example, absorption bands in the benzoic acid spectrum are characteristic of its molar absorptivity at each wavelength.

The Beer–Lambert law can be used to determine the unknown concentration, if the absorbance and molar absorptivity at a particular wavelength are known.