A series of pH optic sensors based on absorption spectra were prepared by immobilizing 6 dyes on anion exchange membranes and attaching the membranes to the end of a bifurcated fiber-optic bundle. The agreement between theory and experiment is excellent. Immobilization leads to the change in dissociation constant of dyes and causes shifts in absorption spectra of dyes. The 6 dyes used are bromophenol blue, bromocresol green, nitrazine yellow, bromocresol purple, o-cresol red and thymol blue; pH 1.6-11.0 can be determine The characteristics of sensors and some factors which affect the characteristics were investigated.

Key words: OPTICAL WAVEGUIDE FIBER, DYES, SENSORS, ION EXCHANGE FILM, BROMOCRESOL GREEN, BROMOCRESOL PURPLE, ACID - BASE INDICATORS, BROMOPHENOL BLUE, DYE IDENTIFICATION, NITRAZINE YELLOW