Reversible and selective detection of NO2 by means of optical fibres

A sandwich-type metal diphthalocyanine, bis(pthalocyaninato)titanium(IV) [Ti(Pc)2], is proposed as a selective chemical transducer for the optical detection of nitrogen dioxide (NO2). An alumina disc was used as a solid support for the immobilisation of the transducer, by means of evaporation from a Ti(Pc)2 solution in toluene, and was placed in a suitable flow-cell. Through interaction with nitrogen dioxide, this compound underwent spectral changes in the red and green components of the visible spectrum. The optical characterisation of the optode was carried out by an appropriate optoelectronic unit, which was connected to the flow-cell by a single optical fibre. Appropriate treatment with UV light made the optode fully reversible. The optode developed was found to be very selective, and no interference coming from other gases was observed. A detection limit of 0.6 ppm was obtained.