Analytical Sciences

A Variety of Lipophilic Amines Incorporated in Liquid Membranes Exhibit Potentiometric Responses to Neutral Phenols

Takashi ITO*1, Hanna RADECKA*2 , Kayoko UMEZAWA*3 , Tatsuji KIMURA*2 , Akiko YASHIRO*2 ,Xiao Ming LIN*4, Masamitsu KATAOKA*2 , Eiichi KIMURA*5 , Jonathan L. SESSLER*6 ,Kazunori ODASHIMA*7 and Yoshio UMEZAWA*1*

*1 Department of Chemistry,School of Science, The University of Tokyo, Hongo, Tokyo 113, Japan
*2 Department of Chemistry, Faculty of Science, Hokkaido University,Sapporo, Hokkaido 060, Japan
*3 Department of Chemistry, Faculty of Science, OchanomizuUniversity, Bunkyo, Tokyo 152, Japan
*4 Division of Environmental Conservation, Graduate School ofEnvironmental Science, Hokkaido University,
Sapporo, Hokkaido 060, Japan
*5 Department of Medicinal Chemistry, School of Medicine, HiroshimaUniversity, Minami, Hiroshima 734, Japan
*6 Department of Chemistry and Biochemistry, University of Texas atAustin, Austin, Texas 78712-1167, USA
*7 Graduate School of Pharmaceutical Sciences, The University ofTokyo, Hongo, Tokyo 113, Japan

A variety of lipophilic amines incorporated in PVC matrix liquid membranesexhibited anionic potentiometric responsesto phenolic compounds at the pH conditions under which the phenols existmainly or exclusively in their undissociated,neutral forms. The examined lipophilic amines include a macrocyclicpentaamine, tri(decyl)amine, 4,7-diphenyl-1,10-phenanthroline (bathophenanthroline), 4-octadecylpyridine, and sapphyrin.The potentiometric selectivities of themembranes based on lipophilic aliphatic amines (B) reflected the acidity(hydrogen bond donor activity) and lipophilicity(extractability) of the phenols (ArOH), similarly as membranes based onlipophilic quaternary ammonium salts (Q + X - ).The anionic responses were explained on the basis of a decrease in thecharge separation of protonated amines (BH +) andtheir counteranions (X - ) acrossthe membrane interface. Possible processes leading to a decrease in thecharge separationbetween BH + and X - are (i) complexation between ArOH and BH+ X -, followed by proton dissociation and ejection of HXinto the aqueous phase, as well as (ii) complexation between ArOH and B.The membrane based on sapphyrin showed ahigh potentiometric selectivity to catechol, possibly due to geometricaldiscrimination of the ortho dihydroxy structure ofcatechol by the nitrogen(s) on the rigid macrocyclic structure of sapphyrin. (Keywords: Liquid membrane electrode, lipophilic amine, potentiometricresponse, phenolic analyte,response mechanism)

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