SYNTHESIS AND CHARACTERIZATION OF NEUTRAL HYDROGEN ION-SELECTIVE CHROMOIONOPHORES FOR USE IN BULK OPTODES

The type of ion-selective sensors discussed is based on a solvent polymeric membrane with optical transduction (bulk optode), and requires a reversible mass transfer of analyte ions into and from the bulk of the organic phase. Apart from the ion to be analysed, such sensors simultaneously measure a reference ion. For analytical purposes, an H+-selective carrier absorbing light in the visible range (chromoionophore) is incorporated in the membrane together with an ionophore as known from ion-selective electrodes. A series of neutral H+-selective chromoionophores, synthesized with a view to their possible use in bulk optodes, are described. The results of various studies on the basicity in different solvents, lipophilicity, chemical stability, selectivity, molar absorption coefficients and absorbance maxima are given and, in part, discussed theoretically. It is shown that the chromoionophores described are highly selective and offer a wide range of basicities. Their lipophilicity usually guarantees a long lifetime for applications in both aqueous solutions and diluted blood and serum, but for measurements in undiluted blood samples they should be covalently immobilized to the polymer of the optode membrane. Their chemical stability is usually sufficient, only direct sunlight causing rapid decomposition.