Figure 9.1
(a) Double-beam recording UV/visible spectrophotometer.
(b) Double-beam recording IR spectrophotometer.
(Courtesy of Beckman Instruments, Inc., Fullerton, California.)incident radiation can be related to the concentration of absorbing species and to the thickness of the
absorbing medium, both relations being embodied in the Beer-Lambert law.
Derivation of the Beer-Lambert Law
Lambert's law, which concerns the thickness of an absorbing medium, states that successive equal
thicknesses absorb equal fractions of monochromatic incident radiation. This leads to an exponential
decrease in the intensity of the radiation as it passes through the layer. In mathematical terms,
where I 0 and I are the incident and transmitted intensities respectively, l is