Iso-absorptive point

Graphical Absorbance Ratio Method. The method of Hirt et al. quickly gives the relative concentration of two components without solving simultaneous equations. It is most convenient when the two components spectra exhibit an iso-absorptive point, a wavelength at which the spectra cross each other, showing that the compounds have equal absorptivities. 

A linear calibration curve can be plotted from a knowledge of the ratios of absorbance at the analytical wavelength to that at the iso-absorptive point for the two pUre materials or for any two known mixtures thereof. 

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