Abstract
The conductometric sensor based on 25,27-di-(5-thio-octyloxy)calix[4]arene-crown-6 was developed for the quantitative analysis of ammonium. The calixarene was immobilized on the surface of the planar interdigitated electrodes by attachment of its dialkyl sulfide groups to the surface of the gold electrodes. The intrinsic ability of the calixarene to capture ammonium was studied in the conductometric measuring mode and by the electrochemical impedance spectroscopy. The developed sensor showed high selectivity to ammonium in the presence of mono-, di-, and trivalent cations. Selective and highly sensitive detection of ammonium resulted from the complexation between the ammonium ions and a crown-ether fragment of the upper rim of the 25,27-di-(5-thio-octyloxy)calix[4]arene-crown-6 macrocycle. The developed sensor had high signal repeatability. Its sensitivity was found to be satisfactory for the forthcoming sensor application in the water-sample analysis; the linear range was 0.01–1.5 mM and limit of detection 10 μM.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1317-9) contains supplementary material, which is available to authorized users.
Highlights
Nowadays, an increase in the ammonium concentrations in the surface water systems causes a significant environmental and economic concern
New analytical tools based on the chemical entities capable of inducing selective binding and transport of ionic or neutral species are of growing interest nowadays
The lipophilic benzene rings of the cavity protect the ammonium cation against hydration, enhancing the ion-dipole and hydrogen bonds in the supramolecular “host-guest” complex. As we showed it earlier, ammonium can be quantitatively determined with natural zeolite immobilized on the surface of the conductometric interdigitated transducers [7]
Summary
An increase in the ammonium concentrations in the surface water systems causes a significant environmental and economic concern. Two nitrogen forms coexist in a certain ratio. New analytical tools based on the chemical entities capable of inducing selective binding and transport of ionic or neutral species are of growing interest nowadays. Being the phenolic [1]nmetacyclophanes obtained by the high-precision cyclo-condensation of the p-substituted phenols with formaldehyde, calix[n]arenes possess intramolecular lipophilic cavities formed by aromatic rings of the macrocyclic skeleton. The structural diversity of calix[n]arenes is stipulated by their conformational isomerism
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