ACCUMULATION AND VOLTAMMETRIC DETERMINATION OF COMPLEXED METAL-IONS AT ZEOLITE-MODIFIED SENSOR ELECTRODES

Chemically modified electrodes based on zeolite-containing graphite pa stes were constructed and evaluated as sensor electrodes for the volta mmetric determination of traces of metallic species in solution. Zeoli te molecular sieves with pore sizes of 3, 4, 5, and 10 Angstrom were a ll suitable for chemical deposition and subsequent voltammetric quanti tation of traces of Cu(II), Cd(II), and Zn(II). The highest sensitivit y was obtained using the zeolite with the 10 Angstrom pore size. The d etection limit obtained for Cu(II) was 0.3 mu M following a 2 min chem ical deposition. The detection limits for Cd(II) and Zn(II) following a 4 min chemical deposition were 87 nM and 145 nM, respectively. The e ffects on the zinc signal of coexisting metallic species in the ammoni a deposition medium were studied. While the addition of Hg(II) gave ri se to increasing zinc signals, the addition of Ag(I), Cu(II), Cd(II), Ni(II), and Co(II) resulted in decreasing zinc signal amplitudes. Most notably, the magnitude of the interference from these latter metal io ns correlated well with the coordination numbers of their ammonia comp lexes. Thus the electrode acted as a device which was sensitive to the size and shape of the interfering metal complex.