Analytical Sciences

Potentiometric Responses of Polymeric Liquid Membranes Based on Hydrophobic Chelating Agents to Metal Ions

Yasoo ITOH,* Yoshihisa UEDA,* Ayumi HIRANO,** Masao SUGAWARA,** Koji TOHDA,** Hideo AKAIWA,*** and Yoshio UMEZAWA** 

*Hokkaido Institute of Public Health, Sapporo 060-0819, Japan
**Department of Chemistry, School of Science, The University of Tokyo, Tokyo 113-8656, Japan
***Administration Office, Gunma University, Maebashi 371-8510, Japan

The effect of hydrophobicity of acidic chelating agents as sensing materials on the potentiometric responses of polymeric liquid membranes was investigated. The chelating agents tested were 8-quinolinol (HOx), dithizone (HDz), 1-(2-pyridylazo)-2-naphthol (PAN) and their alkylated analogues, 5-octyloxymethyl-8-quinolinol (HO8Q), di(p-hexylphenyl) thiocarbazone (C6HDz), 7-pentadecyloxy-1-(2-pyridylazo)-2-naphthol (C15PAN) and a series of N-alkylcarbonyl-N-phenylhydroxylamines (CnPHA, n = 3, 6, 9, 12). The distribution coefficients between membrane solvent and water were determined to evaluate the hydrophobicity of the agents. The potential-pH profiles of the membranes containing hydrophobic chelating agents demonstrated the generation of potentiometric responses, while less hydrophobic agents gave no response. A possible model for the generation of membrane potential is proposed. The charge separation is attained by the permselective uptake of metal cations by the chelating agent anion at membrane/solution interface, where the high hydrophobicity of the agent enables the anionic or deprotonated form of the agents to remain at the membrane/solution interface.

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