Patent ID: 7807473

Claim:
A method of quantitatively measuring the concentration of chlorine in a sample solution with a sensor film, said method comprising: preparing a hydrogel sensor film having a chemical composition comprising an indicator that changes its optical properties upon being exposed to the chemical species in the sample solution; adding a polymer super acid additive during the formation of the hydrogel sensor film such that the polymer super acid additive mixes with the indicator and hydrogel of the sensor film; immobilizing the indicator in the hydrogel film by forming an ion pair between the indicator and a quaternary ammonium, quaternary phosphonium, quaternary imidazolium, quaternary pyridium, quaternary pyrrolidinium, or quaternary sulfonium ion, wherein the concentration of quaternary ammonium, quaternary phosphonium, quaternary imidazolium, quaternary pyridium, quaternary pyrrolidinium, or quaternary sulfonium salt is 5-1000 times greater than the stoichiometric amount required to ion pair the indicator; exposing the film to a fixed amount of the sample solution; measuring the absorbance of the film at a wavelength near the maximum absorbance peak (λmax) of the indicator using optical scanning equipment; and quantifying the concentration of the chemical species in the sample solution using the average absorbance measured from the sensor film.