New calibration models for the determination of 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-l,l0- phenanthroline) octylsulfonate (Ru(dpp)OS),1 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 life-time giving the dimensionless 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 Stern-Volmer (SV) calibration approach (model (I)) was compared with two alternative models based on the inflection point of the light emission profile (model (II)) and on a suitable integral of the light emission profile (model (III)). Regression parameters P1 and P2 were determined and their physical meanings were explained with digital simulation techniques enlightening the nature of the chosen approaches.3 Sensitivity, precision and working interval of the three membranes were studied. Model (I) fails for low oxygen percentage values, 2 %O , (depending on luminophore nature) whilst the other two works well in the whole 0-100 2 %O range. Model (I) works up to 100%, 93% 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 the 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. A dimensionless kinetic constant, = 2.25(0.09) kg , valid for all membrane typologies was determined. It allowed the evaluation of the membrane thickness.