Beer-Lambert Law:
Beer-Lambert Law states that optical absorbance of the chromophore in a transparent solvent varies linearly with the sample cell path length and the chromophore concentration both. The law relates absorption of the light to the properties of the material through which the light is traveling. The Beer-Lambert law is linear relationship in between absorbance and concentration of an absorber of the electromagnetic radiation. The general Beer-Lambert law is generally written as:
A= aλ x b x c
where A is the measured absorbance, aλ is a wavelength-dependent absorptivity coefficient, b is path length, and c is analyte concentration
Beer's law is only valid if the following conditions are satisfied: The absorbers should act independently from each other; The absorbing medium should be homogeneously distributed in the interaction volume and should not scatter the radiation; The incident radiation should consist of parallel rays, each traversing the same length in absorbing medium; The incident radiation should preferably be monochromatic, or have at least a width which is more narrow than the absorbing transition; and The incident flux should not influence the atoms or molecules; it should act as a non-invasive probe only of the species under study. Particularly this implies that the light should not cause optical saturation or the optical pumping, since such effects will deplete the lower level and possibly give rise to the stimulated emission. If any of theconditions are not fulfilled, there will be deviations from the Beer's law.
Beer's law is nonlinear as there are deviations in the absorptivity coefficients at high concentrations (>0.01M) because of electrostatic interactions between molecules in close proximity; scattering of light because of particulates in the sample; fluoresecence or phosphorescence of the sample; changes in the refractive index at high analyte concentration shifts in the chemical equilibria as a function of concentration; and non-monochromatic radiation, deviations are minimized by using a relatively flat part of the absorption spectrum like the maximum of an absorption band stray light.