Calibration models under dynamic conditions for determining molecular oxygen with optical sensors based on luminescence quenching of transition metal complexes embedded in polymeric matrices

Three oxygen-sensitive polysulfone-based membranes employing ruthenium tris(4,7-diphenyl-1,10-phenanthroline) octylsulfonate (Ru(dpp)OS), 5,10,15,20-tetraphenyl-21H,23H-porphyrin platinum(II) (PtTPP), and 5,10,15,20-tetrakis(pentafluorophenyl)-21H,23H-porphyrin palladium(II) (PdFTPP) were prepared and tested with different calibration approaches. The three luminescent labels were chosen for their different lifetimes giving the dimensionless Stern-Volmer (SV) constant, K′SV, of 0.0176(0.0001), 0.146(0.001), and 1.768(0.014) for Ru(dpp)OS, PtTPP, and PdFTPP, respectively. The usual SV calibration approach, model I, was compared to two alternative dynamic models on the basis of the light emission profile. Model II was based on the inflection point, and model III was based on a suitable integral of the light emission profile. Regression parameters were determined, and their physical meanings were explained with digital simulation techniques enlightening the nature of the chosen approaches. Sensitivity, precision, and working interval of the three membranes were studied. Model I fails for high oxygen percentage values, %O2 (depending on luminophore nature), while the other two work well in the whole 0-100 %O2 range. Model I works up to 98%, 50%, and 25% oxygen with Ru(dpp)OS, PtTPP, and PdFTPP, respectively. Model II is more sensitive than model I for %O2 < 60%, < 6%, and < 2% for Ru(dpp)OS, PtTPP, and PdFTPP membranes, respectively. Precision of model I is almost constant as foreseen for a linear model. Averaged experimental precision values of 3.5, 0.7, and 0.4% were found for Ru(dpp)OS, PtTPP, and PdFTPP, respectively. An averaged dimensionless kinetic constant valid for all membrane typologies was determined. It allowed the evaluation of the membrane thickness.