A novel optical chemical sensor was constructed for measurement the concentration of Hg2+ ion in solutions by covalent immobilization of thiazole yellow dye on a triacetyl cellulose film via epichlorohydrin as a linker. The chemical interaction between the Hg2+ ion and immobilized thiazole yellow molecules was studied by UV-Vis spectrophotometry at 420 nm. The effect of influencing parameters on immobilization of the dye molecules on the surface of the film and also for improving the sensitivity of the constructed optode was studied. The optode showed a dynamic range from 1×10-7 to 3.2×10-5 M with respect to concentration of Hg2+ ion at pH 9 and its limit of detection was found to be: 1×10-8 M. The fabricated optical chemical sensor has good analytical performance such as good selectivity and sensitivity, adequate short term and long term stability and a good reproducibility and repeatability. The response of the fabricated sensor to Hg2+ ion is completely reversible and it can be regenerated easily at pH 5 buffer solution in about 2 minutes. Its response time is 12 min. The constructed optode was successfully applied for determination of Hg2+ ion in real samples.

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