Soluble phthalocyanines as suitable coatings for highly sensitive gas phase VOC-detection

The interaction of modified phthalocyanines (PCs) was studied with benzene, toluene, m-xylene and n-octane by using thickness shear mode resonators (TSMRs). The n-octane showed linear sorption isotherms, whereas the aromatic compounds revealed extremely nonlinear adsorption isotherms with high intensities at low concentrations. The nonlinear isotherms are described in a theoretical model by assuming selective and unselective sorption and by combining Langmuir- and Henry-type of sorption isotherms. The sorption of all aromatics takes place in the bulk as it is deduced from the proportionality of the sensor signals with coating thickness. To indicate the high sensitivity, the calculated limit of detection for a phthalocyaninatoplatin(II)coating was 0.5 ppm for benzene and 0.2 ppm for toluene.