Molar absorptivity and the blank correction factor.

In photometry, where both the product formed and one or several reactants absorb light at the same wavelength, the absorbance of the "blank" of the sample at the end of the reaction may be less than that measured at the beginning of the reaction, because of consumption of reactant(s). The blank correction factor for the determined result with one light-absorbing reagent is epsilon P / (epsilon P - epsilon R), where epsilon R and epsilon P are the molar absorptivities of the reagent and the product, respectively. We derived a factor for the case when more than one reagent absorbs light at the same wavelength as the measured product. This factor is independent of the concentration of reagent(s) and can correct the determined result or absorbance for the consumption of light-absorbing reagent(s) during the reaction.