2CLabManual201303

As indicated by the equation of beers law shown above

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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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