Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10410987 | Sensors and Actuators B: Chemical | 2005 | 7 Pages |
Abstract
The upper rim of calix[6]arene-hexaacetic acid hexaethyl esters was modified with various alkyl substituents to develop ionophores for constructing organic ammonium ion-selective membrane electrodes. We found that the substitution of bulkier alkyl groups enabled a more effective discrimination of simple aliphatic ammonium ions such as methylammonium and ethylammonium. In particular, an electrode based on p-1,1,3,3-tetramethylbutylcalix[6]arene-hexaacetic acid hexaethyl ester showed the highest response to methylammonium among various organic ammonium ions and inorganic cations, giving the following selectivity coefficients; logkCH3NH3+,XPot: C2H5NH3+, â0.2; C3H7NH3+, â1.4; C4H9NH3+, â1.9; C6H13NH3+, â1.6; phenethylammonium, â1.9; Na+, â2.8; K+, â1.8; Rb+, â1.6; Cs+, â0.2; NH4+, â2.8. The electrode exhibited a near Nernstian response to methylammonium in the concentration range of 1Â ÃÂ 10â5 to 1Â ÃÂ 10â2Â M with a slope of 58.5Â mV per concentration decade in 0.1Â M MgCl2. The limit of detection was 3Â ÃÂ 10â6Â M. The electrode could be used over a pH range of 2-10. Formation of a 1:1 complex between p-1,1,3,3-tetramethylbutylcalix[6]arene-hexaacetic acid hexaethyl ester and methylammonium was confirmed by electrospray ionization mass spectrometry. The response characteristics of the methylammonium-selective electrode were compared with those of NH4+-selective electrodes so far developed.
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Authors
Keisuke Ueda, Hideaki Hioki, Miwa Kubo, Mitsuaki Kodama, Kiyoka Takaishi, Hirochika Yokosu, Takashi Katsu,