LUMINESCENCE LIFETIME QUENCHING OF A RUTHENIUM(II) POLYPYRIDYL DYE FOR OPTICAL SENSING OF CARBON-DIOXIDE

Carbon dioxide in gaseous samples can be measured in the 3.5 x 10(-4) to 0.1 MPa partial pressure range with the use of a fiber-optic lumine scent sensor operated in the time-correlated single photon counting (T C-SPC) detection mode. The sensitive tip is fabricated with tris[2-(2- pyrazinyl)thiazole]ruthenium(II) electrostatically immobilized onto ca rboxymethyl-Sephadex gel. The photoexcited dye is dynamically quenched by hydrogenphthalate generated upon permeation through silicone and d issolution of CO2 into the indicator gel phase containing phthalate bu ffer of pH 7.3. The nonlinear response of the optical indicator is sho wn to obey the calculated complex relationship between its emission li fetime and the P-CO2. Luminescence decays (293 > tau > 173 ns) of the polymer-supported indicator are strictly exponential in the 0-100% CO2 range. Relative standard deviation values (n = 7) of 1.9, 1.2, and 1. 7% have been measured for 0.0044, 0.023, and 0.092 MPA CO2 in argon, r espectively; almost twice as much were obtained when the sensor was op erated in the emission intensity mode. The temperature effect (6.1 ns K-1) on the sensitive membrane and (linear) cross-sensitivity to oxyge n are discussed as well. The working principle put forward allows one to monitor CO2 using the same optoelectronic instrumentation already w ell developed for phase-sensitive luminescence optosensing of O-2 with pH independent Ru(II) indicators.