HYDRATION OF TRIFLUOROACETOPHENONES AS THE BASIS FOR AN OPTICAL HUMIDITY SENSOR

The reversible hydration of trifluoroacetophenones was taken as the basis for the construction of a new kind of humidity sensor. Since this hydration is followed by a change in the absorption spectrum of the acetophenone isologues, a straightforward optical transduction in the UV range was possible. Plasticized poly(vinyl chloride) (PVC) membranes that incorporate such electrically neutral and lipophilic compounds together with a quaternary ammonium salt (MTDDACI) as a catalyst exhibit a series of impressive characteristics. These so-called optode membranes show an excellent selectivity for humidity over other gases, a high stability, good reproducibility, a very short response time in the range of seconds, and a wide measuring range, which can easily be changed by the introduction of different substituents in the para position to the trifluoroacetyl group. With two isologue ligands, a determination of relative humidity (RH) in the range from 1% to 100% RH with a high precision was possible.