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Unformatted text preview: sorptivity versus
wavelength is called the absorption spectrum of the substance.
Beer's Law forms the basis for the analytical use of spectroscopy to determine concentrations. As indicated by the equation of Beer’s Law shown above, a plot of the absorbance
at a given wavelength for a particular species versus the concentration of the species
yields a straight line with a slope equal to ℓ and an intercept of zero. Since the path
length of the cell used for the absorbance measurements is typically known, the molar
absorptivity of the species at a chosen wavelength is readily determined from such a
Beer's Law plot. The concentration of the species in an unknown sample can then be
determined by measuring the absorbance of the sample at the same wavelength in any
cell of known path length.
The wavelength for such an analysis should be chosen so that small changes in
wavelength do not yield large changes in absorbance. Namely, the chosen wavelength
should be in a relatively flat portion of the absorption spectrum. Typically, a wavelength
associated with a maximum in the spectrum is chosen, si...
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- Spring '07