Beer's law states A=ebc, which directly relates the concentration(c) of a sample, its molar absorptivity (e) and the absorbance(A) of a sample. Instead of bothering with a standard curve why not make two measurements: first, measure the A of a sample of known concentration in order to compute e. second, measure the absorbance of the solution with un-known concentration and use the e from the first calculation to calculate the concentration.
Would this be a better method than doing the standard curve with different measurements. Why or why not?