An optical chemical sensor was developed for the determination of Fe3+ based on the reversible fluorescence quenching of 5-tret-Butyl-2-methoxy thiacalix[4] arene(Tc4A-OCH3) immobilized in a plasticized poly(vinyl chloride)(PVC) membrane.The optimum membrane of the sensor is composed of 50 mg of PVC,100 mg of bis(2-ethytbexyl) sebacate(DOS) and 2.5 mg of 5-tret-Butyl-2-methoxy thiacalix[4] arene.The maximum response of the optode membrane for Fe3+ was obtained in pH of 7.0 potassium chloride solution.Under the optimum conditions des...