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-acce pting gases such as chlorine. Our preliminary investigations using vac uum sublimed films of 5,10.15,20-tetraphenyl-porphin (H2TPP) have show n that a fluorescence decrease can be observed when the films are expo sed to chlorine gas at low concentrations (ppm). Unfortunately vacuum sublimed films of H2TPP produce only a weak fluorescence emission. H2T PP dissolved in silicone rubber films exhibits a strong fluorescence e mission which makes the films more suitable for optical measurement. I n addition, the non-polar environment favours a protonation reaction i n which H2TPP is converted to the diacid dication, H4TPP2+. This is th e sensing interaction used to detect and measure chlorine gas which ca n be followed either by monitoring the fluorescence decrease from H2TP P or the fluorescence increase from H4TPP2+. Equilibration of :he film s does not occur, however, the interaction is suited to a kineto-optic al method of measurement. The films respond quickly, reversibly and re producibly with the kineto-optical method requiring only a short expos ure period.