A KINETO-OPTICAL METHOD FOR THE DETERMINATION OF CHLORINE GAS

The redox and optical properties of porphyrins make them particularly interesting and useful as potential chemical sensors for electron-accepting gases such as chlorine. Our preliminary investigations using vacuum sublimed films of 5,10.15,20-tetraphenyl-porphin (H2TPP) have shown that a fluorescence decrease can be observed when the films are exposed to chlorine gas at low concentrations (ppm). Unfortunately vacuum sublimed films of H2TPP produce only a weak fluorescence emission. H2TPP dissolved in silicone rubber films exhibits a strong fluorescence emission which makes the films more suitable for optical measurement. In addition, the non-polar environment favours a protonation reaction in which H2TPP is converted to the diacid dication, H4TPP2+. This is the sensing interaction used to detect and measure chlorine gas which can be followed either by monitoring the fluorescence decrease from H2TPP or the fluorescence increase from H4TPP2+. Equilibration of :he films does not occur, however, the interaction is suited to a kineto-optical method of measurement. The films respond quickly, reversibly and reproducibly with the kineto-optical method requiring only a short exposure period.