Beer-Lambert Law Spectrophotometry
Quantify the linear relationship between solute concentration, optical path length, and radiant light absorbance.
Dimensionless optical density
Photometric Principles & Absorbance
The Beer-Lambert law establishes that the absorbance of radiant energy by an absorbing chemical species in solution is directly proportional to its molar concentration and the optical path length traversed:
Here, A is the unitless absorbance (optical density), ε is molar absorptivity (L mol⁻¹ cm⁻¹), c is solute molar concentration (mol L⁻¹), and l is the path length in centimeters.
Model Assumptions & Optical Limitations
- Monochromatic radiant beam perpendicularly incident on parallel planar optical surfaces.
- Absorbing chromophore species act independently without intermolecular aggregation.
- Homogeneous solution without light scattering particulate suspensions.
Frequently Asked Questions
When does the Beer-Lambert law deviate from linearity?
Deviations occur at high concentrations (>0.01 M) due to electrostatic interactions between chromophores, refractive index shifts, or chemical equilibria such as dimerization.
What is molar absorptivity (ε)?
It is an intrinsic molecular property reflecting how intensely a specific chemical species absorbs light at a given wavelength.
More from Alok Das
These interactive tools are personal side-projects built for exploration and utility. My primary professional commitment is in M.Sc. Chemistry, analytical research, and laboratory methodology.