Design and Characterization of a Novel Ammonium Ion Selective Optical Sensor Based on Neutral Ionophores

A novel principle of an optical sensor (optode) has been realized in practice by combining NH_4^+-selective neutral ionophores of the macrotetrolide type, H^+-selective neutral chromoionophores that drastically change their absorption spectrum upon protonation, and lipophilic anionic sites in the same plasticized PVC membrane. Such chemical sensors generally offer the advantages of a highly selective and reversible recognition of given ionic substrates and of a straightforward optical transduction of the recognition process. The present membrane exhibits the theoretically expected absorbance response to ammonium ions in pH-buffered samples. Dynamic range, selectivity coefficients, reproducibilities, and response times of the new optode system are promising in view of analytically relevant applications.