Patent CA-1309876-C (CA)
Title: Method and composition for measuring oxygen concentration
Inventor: KHALIL GAMAL-EDDIN
IPC: G01N21/76
Filed: 1986-07-02
Granted: 1992-11-10
Abstract: METHOD AND COMPOSITION FOR MEASURING OXYGEN CONCENTRATION                   Abstract Methods and compositions are described for measuring oxygen concentration, particularly for monitoring oxygen in the blood with a fiber optic catheter. Oxygen concentration is determined by observing quenching of the emission from a luminescent (phosphorescent or fluorescent) molecule embedded in oxygen-premeable plastic. A test fluid of unknown oxygen concentration is contacted with a plastic film containing at least one luminescent substance. Thefilm is subjected to irradiation over som eperiod of time by light of a wavelength that is strongly absorbed by the luminescent substance, and a measure of the time dependence of luminescent emission intensity I(t) is obtaned. Three modes modes of determining oxygen concentration from I(t) are described. (i) Subsequent to a brief (approximately 5 µs) flash of light I(ti) is determined by use of a transient recorder and fit to Eq. (6). An average decay rate ? = (A1k1 + A2K2)/(A1 + A2) is determined, and ? used for the Stern-Volmer plot of Eq. (1). (ii) The period of linear decay of luminescent emission is determined from the I(t) data, and that intensity versus time profile is referenced against similarly obtained profiles for reference fluids of known oxygen concentration, using shapes, intensity or time setpoints. (iii) The sample is irradiated for some time interval (generally under 50 µs) using a flash lamp or a light emitting diode. Intensity segments of emission, I1 and I2, are determined during two time intervals defined with respect to the time of irradiation. These two intensity segments are compared to form a ratio R, and a calibration plot of R versus oxygen pressure is obtained using solutions of known oxygen concentration. Three different methods for determining I1, I2, and R are presented. These methods (i-iii) of measuring quenching are insensitive to variation in plastic thickness and emitter concentration of the probe and to decomposition during operation. Methods (i-iii) also take into account the non-exponential decay of the emission, and thus extend the pressure range over which the probe is sensitive. Method (iii) requires at most one point calibration against atmospheric oxygen. Also disclosed are photostable luminescent molecules for use with the subject method. In a preferred embodiment platinum tetra(pentafluoro-phenyl)porphyrin, Pt(TFPP), serves as the luminescent oxygen quenching-sensitive molecule. Pt(TFPP) has a strong absorbance in the visible region, a strong phosphorescence with lifetime of roughly 100 µs, and is photostable. Photostability is provided by the substitution of fluorine atoms in the periphery of the synthetic prophyrin ring. Other suitable fluorinated luminescent molecules include metallo derivatives, particularly platinum and palladium derivatives, of partially or fully fluorinated octaethylporphyrin, tetraphenyl-porphyrin, tetrabenzoporphyrin, or the chlorins, bacteriochlorins, or isobacteriochlorins thereof. The latter reduced porphyrins have the advantage that their absorption is red-shifted to a region for which light emitting diodescan be used for excitation.