2CLabManual201303

One should always establish before its analytical use

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Unformatted text preview: nce at a maximum, the slope of the spectrum is zero or horizontal and simultaneously good sensitivity is obtained in the analysis (significant absorbance for a given concentration). One should always establish, before its analytical use, that Beer's Law is followed by a species over the concentration range of interest, since deviations from Beer's law often occur at high concentrations. Typically, these deviations can be traced to changes in the absorbing species or the bulk solution with concentration. For example, in concentrated solutions the solute molecules are closer together on average and interact with each other, changing their energy levels and spectroscopic properties from a dilute solution. The species of interest also may exist in equilibrium with other species that have different molar absorptivities. In such cases, a graph of absorbance versus concentration will appear to deviate from a straight line at high concentrations. 49 If two species are present, and neither affects the light absorbing properties of the other, then the observed total...
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This note was uploaded on 04/09/2013 for the course CHE CHE 2C taught by Professor Nasiri during the Spring '07 term at UC Davis.

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