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 × 10-4 to 0.1 MPa partial pressure range with the use of a fiber-optic luminescent sensor operated in the time-correlated single photon counting (TC-SPC) detection mode. The sensitive tip is fabricated with tris[2-(2-pyrazinyl)thiazole]ruthenium(II) electrostatically immobilized onto carboxymethyl-Sephadex gel. The photoexcited dye is dynamically quenched by hydrogenphthalate generated upon permeation through silicone and dissolution of CO2 into the indicator gel phase containing phthalate buffer of pH 7.3. The nonlinear response of the optical indicator is shown to obey the calculated complex relationship between its emission lifetime and the PCO2. Luminescence decays (293 > τ > 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, respectively; almost twice as much were obtained when the sensor was operated in the emission intensity mode. The temperature effect (6.1 ns K-1) on the sensitive membrane and (linear) cross-sensitivity to oxygen are discussed as well. The working principle put forward allows one to monitor CO2 using the same optoelectronic instrumentation already well developed for phase-sensitive luminescence optosensing of O2 with pH-independent Ru(II) indicators.