AN OPTOCHEMICAL SENSOR FOR CD(II) AND HG(II) BASED ON A PORPHYRIN IMMOBILIZED ON NAFION(R) MEMBRANES

An optochemical sensor for the detection of Cd(II) and Hg(II) ions in aqueous solutions can be constructed by immobilizing 5,10,15,20-tetra(4-N-methylpyridyl)porphyrin electrostatically onto thin layers (2-3 mum) of Nafion(R), a strongly acidic cation-exchanger. The developed procedure for sensor preparation results in sensitive layers with an excellent chemical and mechanical stability. Since the Nafion(R) membrane quantitatively extracts cations from the solution, the kinetics of the increasing absorption of complexes have been measured. For a measuring time of 20 min the detection limits are 5 X 10(-8) mol/l (6 mug/l) and 2 x 10(-7) mol/l (40 mug/l) for Cd(II) and Hg(II), respectively. After each run the sensors can be regenerated. They show no loss in their sensitivity over a period of four weeks.