FUNCTIONALIZED CYCLODEXTRINS AS POTENTIOMETRIC SENSORS FOR ONIUM IONS

Functionalized, lipophilic alpha-, beta- and gamma-cyclodextrins were synthesized and their suitability as onium ion-selective, potentiometric sensors investigated. Selective binding was apparent for NH4+, NMe(4)(+) and NE(4)(+) ions with peroctylated alpha-, beta- and gamma-cyclodextrin, respectively. The phenomenon of complexation was evidenced by H-1 and N-14 nuclear magnetic resonance relaxation-tine measurements and by electrospray mass spectrometry. Nernstian responses were also evident for acetylcholine chloride, dopamine hydrochloride and the surfactant myristyltrimethylammonium bromide. A particularly good sensor for NMe(4)(+) is peroctylated beta-cyclodextrin with o-nitrophenyl octyl ether as plasticizer. A sensitivity of 60 mV decade(-1) was found at 310 K, with a limit of detection, -log a, of 5.8, and -log k(ij)(pot) for Na+, 3.8, for K+, 3.2, and for NH4+, 3.5. The response of 'blank' membrane electrodes comprising poly(vinyl chloride), solvent mediator, and additive was compared with the equivalent electrode response for membranes containing functionalized cyclodextrins. In each instance, the electrode response was substantially enhanced and stabilized by the presence of the lipophilic cyclodextrin. The effect of using either 1.0 mmol dm(-3) NMe(4)Cl or 0.01 mol dm(-3) analyte as inner filling solution was compared, and, with 1.0 mmol dm(-3) NH4Cl, was found to enhance electrode performance.