Practice question

Beer-Lambert law expresses absorbance as A = ε c l, where ε denotes molar extinction coefficient reflecting transition probability, c molarity and l optical path in centimeters. Rearranging yields ε = A divided by (c l). Since absorbance is dimensionless, ε units must compensate concentration times length. Thus dimensions become liter per mole per centimeter, L mol-1 cm-1, frequently written M-1 cm-1. This constant is characteristic for each chromophore such as NADH at 340 nm 6220, tyrosine, tryptophan and nucleic acids. Consistent use of these units ensures reproducibility, inter-laboratory comparison and accurate calculation of biomolecule concentrations.