© 2002 J.Paul Robinson, Purdue University
Absorbance
•O.D. units or absorbance is expressed in logarithmic terms so they
are additive.
•E.g. an object of O.D. of 1.0 absorbs 90% of the light. Another object of O.D. 1.0 placed in the path of the 10%
of the light 10% of this
light or 1% of the original light is transmitted
by the second object
•It is posssible to express the absorbance
of a mixture of substances
at a particular wavelength as the sum of the absorbances of the components
•You can calculate the cross sectional area of a molecule
to determine how efficient
it will absorb photons. The extinction
coefficient indicates this value
3rd ed. Shapiro p 87
