Application to the investigation of Chemical Sensors properties

The sensors were exposed to the following VOC n-pentane, methanol, benzene, triethylamine and acetic acid. 

Data have been analyzed from a multivariate point of view. In this way the cooperative effects of the different materials is studied and the characteristics of each sensor are easily compared with those of the other sensors. PLS was used as a regression method for calculating the capability of the set of sensors to discriminate between the volatile compounds. Volatile compounds were checked at different concentrations in order to evaluate the response of sensors in a wide concentration range. Nevertheless, the concentration variation tends to shadow the reaction of sensors with analytes, since the sensor response contains both qualitative (sensor analyte interaction) and quantitative (analyte concentration) information. In order to remove the quantitative information, data have been normalized using the linear normalization discussed in section 3. 

The position of the sensors is also of great interest. As argued cavi-tands 1 and 3 lie in the same direction as the alcohol, in accordance with their selectivity towards alcohols. On the other hand, the co-linearity with benzene is not expected. This is a hint that in these cavitands the hydrogen bond interaction is improved but at the same time other kinds of interactions have a comparable magnitude. 

Other sensors are mostly grouped towards the triethylamine. In the case of porphyrins 6-8, 13 the coordinated metal is no longer able to drive the selectivity pattern and the presence of the peripheral alkyl chains completely shadows the coordination interactions. This result can explain the failure to observe the coordination interaction in the sensing mechanism of the metal complexes of the closely related alkyl chains functionalized phthalocyanines reported in the past by Gopel and coworkers [22]. 

In order to better investigate the relationship between sensor response and interaction mechanism it is useful to consider the way in which each volatile compound is expected to interact when in contact with a solid phase. These interactions can be modelled using the linear sorption energy relationship approach (LSER) [23]. 

---