When entrapping indicators in sol-gel materials for optical sensing purposes, one should be careful to take into account that changes in the cage properties, caused by variations in the synthetic procedures, might affect the performance of the dopant. We show - for SiO2 sol-gel entrapped pH and polarity indicators - that such variations are brought about by changing the water-silane r-ratio preparation conditions and by changing the environmental humidity to which the material is exposed. The observations are interpreted in terms of changes in the acidity and polarity of the cage surface.
A new class of sensitive disposable sensors for determination of trace concentrations of water pollutants has been developed. It utilizes porous transparent silica glasses doped with organic photometric reagents. The silica sensors are produced at room temperature by the sol-gel procedure, i.e. by hydrolysis followed by polycondensation of tetraalkoxysilanes. Thus, we produced porous glasses doped with organic photometric reagents for the determination of typical cations, anions, pH, oxidation agents (e.g. disinfection agents) as well as typical air pollutants. A mathematical model for a flat plate monolithic iron sensor was developed and the predicted calibration curves were compared with the experimental response.