Anion selective polymeric membrane electrodes based on metallocenes

Seven types of metallocenes (bis-cyclopentadienyl compounds) were used as anion ionophores for polymeric membrane electrodes and their anion selectivities were examined. The electrodes based on metallocenes exhibited different selectivity behaviour compared with the electrode using a classical anion exchanger such as tetraalkyl ammonium. The selectivity for tetraalkyl ammonium simply obeys the lipophilicity of anions, specifically, hafnocene dichloride exhibited a highly specific response to anions that have π-electrons such as the salicylate ion. This electrode demonstrated a Nernstian response to the salicylate anion ranging from 1 × 10^-3 to 1× 10^-1 M in a buffered solution (0.05 M Tris-H₂SO₄) adjusted to a pH of 7.4.