Fading Spectrophotometric Method for the Determination of Polyvinylpyrrolidone with Eosin Y

In weak acid medium, eosin Y (EY) has a strong absorption band in the visible light region, and the maximum absorption wavelength (λ_max) is at 517 nm. There is no light absorption for polyvinylpyrrolidone (PVP) in 250–700 nm. When EY was reacted with PVP to form a binding product, a fading reaction of EY appeared and the maximum fading wavelength was still located at 517 nm. At the same time, a smaller absorption peak was observed at 545 nm. The extent of the fading (ΔA) is directly proportional to the concentration of PVP in the range of 0.40–3.20 mg· L^?1. The fading reaction has high sensitivity. The molar absorptivity (ε) is 6.4×10⁶ L·mol^?1·cm^?1 and the detection limit for PVP is 0.12 mg·L^?1. The influencing factors for the reaction have been studied, and the results show that the selectivity is good. Based on this fact, a new fading spectrophotometric method for the determination of PVP with EY has been developed, which is simple and rapid, and it can be applied to the quantitative determination of PVP in beer samples.