Detecção de O2 através de provas fosforescentes com elevada resolução temporal

Abstract

This work presents a new gaseous oxygen sensing system based on time resolved phosphorimetry. The instrument is designed based on a violet LED (low power) and a high sensitivity photomultiplier module. The arrangement has the objective of characterizing new O2 optical transducers with high degree of dynamic suppression and large useful area, specifically palladium and iridium metalloporphyrins immobilized on polymeric films (8 µm thick) of moderate permeability. The primary sensor elements were based on the incorporation of palladium(II) and iridium(III) meso-tetrakis(pentafluorophenyl)porphyrins (PdTFPP and Ir(TFPP)Cl(CO), respectively) into polystyrene (PS) and polycarbonate (PC). Also, it was added to the sensor phases of PdTFPP/PS, nanoparticles of TiO2 and Al2O3, as well as the antenna chromophore coumarin 153. The performance of the sensing system and the production of the optodes are presented along with the optical properties of their probes and main parameters, such as emission intensities, lifetimes, calibration curves, stability and recovery times. The developed system has possibilited detection of lifetimes with good repeatability, even at concentrations of O2 considered high for such compositions (uncertainty of about 1% to 21% of [O2]). For the polycarbonate membranes values of <τ0>/<τ21%> were 4.1 and 26.8, with Ir(TFPP)Cl(CO) and PdTFPP, respectively. For polystyrene, these ratios were 6.3 and 35.9. The lifetime τ0 for the iridium complex exceeded 100 µs in both polymers, while for the PdTFPP indicator it was more than 1000 µs. In general, Stern–Volmer curves showed good linearity (r2 > 0.9966), but a more adequate adjustment of the measured lifetimes ratios was obtained from the Lehrer model (monoexponential decays) and Two-site model (biexponential). The use of the additives produced intensity gains of more than 2x (Al2O3 and coumarin 153) and 3x (TiO2), as well as a photodecomposition reduction for the transducers of about 30% (except coumarin). Furthermore, recovery times t95%↑ were about 3 s for PS, and less than 10 s for PC. Due to the low excitation energy applied, the photodegradation of the transducers was not detected in normal operating conditions, corroborating the feasibility of using the system in applications with continuous monitoring (e.g., human respiration). In summary, pulse phosphorimetry combined with a high sensitivity photodetector has show potential advantages: (i) higher dynamic range, (ii) extended resolution (Δτ/Δ[O2]) and (iii) high operational stability. Furthermore, Ir(TFPP)Cl(CO) constitutes a promising new alternative to O2 detection, providing good stability and potentially intermediate sensitivity to platinum and palladium metalloporphyrins.