Optical sensors are devices which convert a chemical property to a signal. These sensors compared to electrochemical sensors, are free from electrical interferences. On the other hand ease of fabrication for determination of  various ions in aqueous and organic samples are other advantages of these sensors. In this work, an ion optical sensor for determination of Pb(II) and Hg(II) is reported. 4-Hydroxy salophen immobilized on cellulose acetate film. Cellulose acetate film had previously been subjected to a base hydrolysis and then 4-Hydroxy salophen was immobilized on it. This film is shows a maximum absorbance peak at 388 nm. The absorbance spectra of the optode membranes in Pb(II) and Hg(II) solution shown a new peak at 434 nm and 429 nm, respectively, and this property was used as analytical criteria.

The effect of different parameters, such as time of hydrolysis, concentration of 4-Hydroxy salophen, immobilization pH, complexation pH, and contact time were investigated under the optimal conditions. The response time of the optode thin film was 10 min for Pb(II) and 5 min for Hg(II), respectively to reach 98% of final signal. At optimal condition the optode has linear dynamic response  range of 1.0 ×10^-7 – 1.0×10^-3 M of Pb(II) ion with detection limit of 1.0×10^-7 M (0.02 ppm) and 1.0×10^-6- 1.0×10^-2 M for Hg(II) ion with detection limit of 5.4×10^-7 M (0.1 ppm). The relative standard deviation for five replicat measurements of 1.0×10^-6 M and 1.0×10^-5M for Hg(II) ion was 1.6% and 2.4%, respectively, and for 1.0×10^-6 M and 2.5×10^-5 M of Pb(II) ion were 2.1% and 3.7%, respectively.