Nanocomposites and nanomaterials

Conductometric sensor based on natural zeolite for ammonium detection in aqueous media with improved selectivity

Saiapina O.Y.1, Dzyadevych S.V.1,2

1 Laboratory of Biomolecular Electronics, Institute of Molecular Biology and Genetics, NAS of Ukraine, Akademika Zabolotnogo Str., 150, Kyiv-03680, Ukraine, 
E-mail: osayapina4@gmail.com
2 Institute of High Technologies, Taras Shevchenko National University of Kyiv, Hlushkova Avenue, 4G, Kyiv-03022, Ukraine

Zeolites in the sensor design have been recently shown to greatly contribute to the analytical characteristics of the devices and their cost. The zeolite network is based on TO4 tetrahedra (T=Si, Al) occupied with counterions – alkali and alkaline earth metal cations (e.g., sodium, potassium, and calcium), water molecules and sometimes small organic molecules. Today, harnessing of the ion-exchange and adsorption properties of zeolites for their use as host structures opens new horizons for detection of analytes in sensor technologies. 
Natural zeolite clinoptilolite was chosen in this work to study its potentiality as a recognition element of a conductometric sensor for ammonium detection. Taking into account the reported selectivity of clinoptilolite toward ammonium (1), we aimed at studying feasibility of the clinoptilolite use as a principal selective element of the sensor for highly sensitive detection of ammonium. For the sensor development, simple and handy immobilization techniques of zeolite deposition were chosen. Sensor sensitivity and selectivity was compared when zeolite was immobilized on the electrode surface by: 1) entrapment in BSA network cross-linked by glutaraldehyde, and 2) adhesion followed by covering with Nafion® film. The sensor performance was estimated in 5 mM phosphate buffer solution using differential mode of conductometric measurements and EIS in the concentration range of ammonium of 0-25 mM. It was found that zeolite immobilization in the presence of BSA resulted in the significantly reduced selectivity of zeolite-based membrane to NH4+ ions when detected in the presence of interfering sodium or sodium ions solely. Later it was concluded that physical immobilization of zeolite together with Nafion®-based coverage, can be more advantageous technique for further application regarding the obtained analytical characteristics of the sensor. 

Jha V.K., Hayashi S. Modification of natural clinoptilolite zeolite for its NH4+ retention capacity // J. Hazard. Mater. – 2009. – 169. – P. 29-35.