OPTICAL SENSORS FOR DISSOLVED SULFUR-DIOXIDE

Colorimetric sensing membranes for the determination of sulfur dioxide were developed and characterized. These films can be used for sensing trace amounts of sulfur dioxide both in the gas phase and in aqueous solutions. Lipophilic pH indicator ion pairs were immobilized in hydro phobic gas-permeable silicone and phenyl substituted ormosil. On expos ure to SO2 the films undergo a visually detectable color change from b lue to yellow. No cross-sensitivity to pH and CO2 was observed. Respon se times depend on the thickness of the sensing membranes, the indicat or concentration in the film as well as on the respective SO2 concentr ation. Membranes with response times of < 1 min (t(90)) were developed . The sensitivity to sulfur dioxide depends on the pK(a) of the indica tor. An increase in the pK(a) results in a lower detection Limit. The new optical SO2 sensors are chemically and mechanically stable and are easy to manufacture. The storage stability of the membranes is at lea st 7 months if stored in the dark.