The UV/Vis spectrum is plotted automatically as a log10(I0/I) ordinate and l (in nanometers) abscissa. An example spectrum is given below.
As you can see from the above spectrum, different concentrations of 2-nitroaniline will give spectra with differing absorbance values. This can make comparing one spectrum of 2-nitroaniline to another spectrum of 2-nitroaniline obtained by someone else difficult. Converting the above plot from an absorbance ordinate to an e ordinate essentially removes concentration dependence from the presentation. The spectrum below illustrates this point. Notice that each spectrum taken at different concentrations are now essentially overlapping each other.
For publication purposes, UV/Vis spectra are often converted to a log(e) vs. l plot. This type of presentation will normalize the absorbance signals so that all are on a similar scale (essentially diminishing intense absorption signals and increasing weak absorption signals).
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