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An Anomalous Behavior of Anion‐Exchange Membranes with Low Concentration of Quaternary Ammonium Sites: An Apparent Selectivity to Bicarbonate and Phosphate, and Its True Nature
Author(s) -
Grekovich Alexander L.,
Mikhelson Konstantin N.
Publication year - 2002
Publication title -
electroanalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.574
H-Index - 128
eISSN - 1521-4109
pISSN - 1040-0397
DOI - 10.1002/1521-4109(200211)14:19/20<1391::aid-elan1391>3.0.co;2-s
Subject(s) - selectivity , ammonium , chemistry , steric effects , membrane , inorganic chemistry , phosphate , plasticizer , bicarbonate , alkyl , ion , tetramethylammonium , organic chemistry , catalysis , biochemistry
It is shown that anion‐selective electrodes with low concentration of quaternary ammonium sites exhibit an apparent response and selectivity to HCO 3 − and HPO 4 2− ions in aqueous solutions. It is, however, detected that none of these ions is the potential‐determining, and the electrodes actually respond to OH − . The selectivity to OH − is due to unidentified anionic impurities in the plasticizer, and vanishes with aging of the electrodes. Additional purification of the plasticizer eliminates the selectivity to OH − , which, however, is restored after intentional addition of negatively charged sites. Quaternary ammonium sites with longer alkyl chains provide higher selectivity to OH − suggesting that this selectivity originates from steric hindrances against bigger anions.