Estimation of the thickness of absorbing layer in optical membrane sensors

A method was developed for the estimation of the thickness of absorbing lay er in sensitive membrane elements containing covalently immobilized indicat ors and used as transducers in pH optrodes. The method is based on an alter native approach to the interpretation of the spectrophotometric curves repr esenting absorbance as a function of pH, which are usually used for determi ning stoichiometric pK(a) of acid-base indicators. It was found that, depen ding on the geometrical parameters of the indicator molecule, the thickness of the absorbing layer may vary from 2 to 6 mu m. The results obtained by the new method were verified for validity.