Influence of the surface polarity of dye-doped sol-gel glass films on optical ammonia sensor response

A sulfonephthalein dye was immobilized in sol-gel-derived thin films fabric ated from mixtures of tetraethoxysilane and methyltriethoxysilane. Evanesce nt wave absorption spectra on optical fibres were monitored on exposure to gaseous ammonia. Analysis reveals nonclassical response behaviour, the exte nt of which is related to the polarity of the glass. This is accounted for in terms of dye solvation and the involvement of the micro-heterogeneous gl ass surface in the indicator reaction. These observations place important r estrictions of the suitability of polar dye/sol-gel-derived glass combinati ons for gas phase analysis. (C) 2000 Elsevier Science S.A. All rights reser ved.