AN OPTICAL SENSOR FOR THE DETECTION OF HEAVY-METAL IONS

An optic-chemical sensor (optrode) for the detection of heavy metal ions has been developed. The sensitive layer consists of 5,10,15,20-tetra(p-sulfonatophenyl)porphyrin covalently immobilized onto a polymeric matrix. Complexation of ions, such as Cd(II), Pb(II) or Hg(II), results in different absorbance spectra and thus changes the reflection behaviour of the sensor. The effect of immobilization on the complexation characteristics of the dye has been studied in the case of Cd(II). Depending on the length of the spacer molecule, the response time of the sensor is about 40 min, which is of the order of the reaction time in solution. The sensor is reversible and its detection limit is 3 x 10(-6) mol/l for Cd(II). The immobilized dye shows different absorbance spectra for Cd(II), Pb(II) and Hg(II), which enables these ions to be detected simultaneously.