Introduction -- The Beer-Lambert law
(or Beer's law) is the linear relationship between absorbance
and concentration of an absorbing species.
The general Beer-Lambert law is usually written
as: A = abc, where A is the measured absorbance, a is a wavelength-dependent absorptivity coefficient (sometimes called ε, also knows as molar absorptivity), b is the cell-path length, and c is the analyte concentration.
When working in concentration units of molarity, the Beer-Lambert
law is where is the wavelength-dependent molar absorptivity coefficient
with units of M-1 cm-1.
Instrumentation -- Experimental measurements
are usually made in terms of
transmittance (T), which is defined as: T = I / Io where I is
the light intensity after it passes through the sample and Io
is the initial light intensity. The relation between A and T is:
Modern absorption instruments can usually display the data
as either transmittance, %-transmittance, or absorbance. An unknown
concentration of an analyte can be determined by measuring the
amount of light that a sample absorbs and applying Beer's law.
If the absorptivity coefficient is not known, the unknown concentration
can be determined using a working curve of absorbance versus concentration
derived from standards.
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