A fiber-optic fluoresensor for ferric ion has been prepared by using the covalently immobilized fluorescent indicator o-aminobenzoic acid on the polyvinyl alcohol [PVA] via cyanuric chloride. PVA is cross- linked with glutaraldehyde in the presence of hydrochloric acid to form a sensing membrane. The fluorescence of o-aminobenzoic acid is quenched by ferric ion at pH=4 which acts as collisional quencher. The response time of the sensor is in the range of second and reversibility is excellent. It has been applied to the determination of iron in aluminum alloys. The limit of detection is 1.4μg.mL^-^1.

Key words: SENSORS, IRON, POLYVINYL ALCOHOL, COVALENT COUPLING, O-AMINOBENZOIC ACID, QUENCHING, FLUORESCENCE