Beer-Lambert Law
The method is most often used in a quantitative way to determine concentrations of an absorbing species in solution, using the Beer-Lambert law:
- ,
where A is the measured absorbance, is the intensity of the incident light at a given wavelength, is the transmitted intensity, L the pathlength through the sample, and c the concentration of the absorbing species. For each species and wavelength, ε is a constant known as the molar absorptivity or extinction coefficient. This constant is a fundamental molecular property in a given solvent, at a particular temperature and pressure, and has units of or often .
The absorbance and extinction ε are sometimes defined in terms of the natural logarithm instead of the base-10 logarithm.
The Beer-Lambert Law is useful for characterizing many compounds but does not hold as a universal relationship for the concentration and absorption of all substances. A 2nd order polynomial relationship between absorption and concentration is sometimes encountered for very large, complex molecules such as organic dyes (Xylenol Orange or Neutral Red, for example).
Read more about this topic: Ultraviolet–visible Spectroscopy
Famous quotes containing the word law:
““... But here there is nor law nor rule,
Nor have hands held a weary tool;
And here there is nor Change nor Death,
But only kind and merry breath,
For joy is God and God is joy.””
—William Butler Yeats (1865–1939)