| Research Abstract |
Though the directivity of the molecular design of the ionophore for alkali and alkaline-earth metal ion has been established, it has not been established for the heavy and transition metal ionophore. In the present work, twenty-three kinds of Schiff bases were characterized by electrochemical measurement to examine the directivity for improving the silver-ion discrimination ability. Among the Schiff bases, N, N'-bis(2'-hydroxyimino-1'-phenylpropylidene)-1, 3-propanediamine, PHO3, derived from α-isonitrosopropiophenone and 1, 3-diaminopropane was found to be the most practical Ag^+-ionophore. That is, PHO3-NPOE^<I)>(plasticizer)-KTpC1PB^<II)>(anion excluder) system PVC^<III)> membrane electrode gave good results with a Nernstian response in accordance with the wide Ag^+ activity change in the activity range 5.0x10^<-7> to 7.9x10^<-7> mol dm^<-3>. The Ag^+ ion selectivity with respect to K^+ ion, -log k^<pot>_<Ag, K> was 3.35 evaluated by fixed interference method, FIM. This electrodes h
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as the only defect to be a short life time in about 20 days. Therefore, methyl moiety of PHO3 was converted in the long-chain alkyl groups in order to improve the lipophilicity. Among the Schiff based having long alkyl unit, N, N'-bis(2'-hydroxyimino-1'-phenylbuthylidene)-1, 3-propanediamine, PHEtO3 based NPOE-KTpC1PB system electrode showed superior performance during an observation period of more than 2 months, though the Ag^+ selectivity coefficient with respect to K^+, was gradually reduced from 4.35 to 2.95 due to the hydrolysis of Schiff bases. Further, to examine the effect of the number of coordination atom on selective complexation with Ag ion, three kinds of tridentate ligands were synthesized and compared with similar quadoridentate ligand, PHO3. 3-(2-pyridyleethylimono)-2-butanoneoxime, Me-PyO3, having one oxime and a pyridine substituent was found to be the best ionophore for Ag ion electrode. The PVC membrane electrode based on Me-PyO3 exhibit good Ag^+ ion selectivity, -logo k^<pot>_<Ag, K>=3.8, comparable to that of quadridentate PHO3, except for pseudo Nernstian response(3.6mV decade^1) with a wide Ag^+-ion activity change in the activity change from 5.0x10^<-7> to 7.9x10^<-2>mol dm^<-3>.
I) : poly (vinyl chloride) ; II) : o-nitorophenyl octyl ether ; III) : potassium tetrakis (4-chlorophenyl) borate Less
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