FLUOROSENSORS FOR AMMONIA USING RHODAMINES IMMOBILIZED IN PLASTICIZEDPOLY(VINYL CHLORIDE) AND IN SOL-GEL - A COMPARATIVE-STUDY

We report on fluorosensors for ammonia using rhodamines incorporated i n plasticized poly(vinyl chloride) (PVC) and in soi-gel matrix. The re sponse of rhodamine B is due to a change in its molecular structure. W hen exposed to ammonia, the rhodamine is converted into a colorless, n on-fluorescent lactone. As a result, the decrease in fluorescence inte nsity is proportional to the concentration of ammonia. To improve sens itivity we make use of fluorescence energy transfer using donor-accept or complexes. Ion pairs consisting of a fluorophore (rhodamine B or te tramethylrhodamine ethyl ester) and an absorber (bromophenol blue) wer e immobilized in PVC and in sol-gel. Response times of the optode laye rs are in the order of 2 to 8 min depending on the ammonia concentrati on and the matrix used. Limits of detection are as low as 0.1 mu g ml( -1) ammonia. The sol-gel is appropriate for use in sensor technology a nd comparable to PVC layers with respect to response mechanism and res ponse time. Sol-gel based ammonia sensors are advantageous over PVC la yers in their storage stability (greater than or equal to 6 months) an d the relative insensitivity to protons in response to ammonia.