Patent ID: 7394544

Claim:
A method for measuring an elution process of a specific component in a process where a preparation containing at least the specific component subject to a change with time in chemical properties after elution and an impurity component not subject to a change with time in chemical properties after elution is eluted into a test liquid, said method comprising: obtaining a ratio of absorbance k of said impurity component and a ratio of absorbance k′ of said specific component at two isosbestic point wavelengths λ 1 , λ 2 in a system including said specific component and its decomposed matter; measuring at each time the absorbance C 1 (t), C 2 (t) in said two isosbestic point wavelengths for said test liquid at plural time points t of the elution process of said preparation and calculating at least one of the absorbances A 1 (t), A 2 (t) of said specific component by using the relations: k×C 2 (t)−C 1 (t)=k×A 2 (t)−A 1 (t) and A 1 (t)/A 2 (t)=k′; and converting the result to an elution concentration.