Optical-fibre sensors for blood gases and pH, based on porous glass tips

Optical-fibre sensors have been developed for the determination of blood gases and pH. Chemical binding of pyrenebutyric acid and 7-hydroxy-4-methylcoumarine-3-acetic acid to a porous tip of a fused silica fibre produces a sensitive measuring device for molecular oxygen and pH. Insertion of the pH sensor into a solution of bicarbonate, entrapped within a polypropylene membrane, yields a pCO(2) sensor. Excitation of the oxygen-sensor tip within the range 340-360 nm yields emission with a maximum intensity at 460 nm. An intensity ratio approximate to 10 between signals measured in pure gas-phase nitrogen and oxygen is obtained. Excitation of the sensitive tip within the range 360-380 nm yields emission with a maximum intensity at 457 +/- 3 nm. The excitation spectrum is red shifted about 19-30 nm relative to that obtained in solution. The maximum intensity of the excitation spectrum for the acidic form of the bound coumarine derivative is at 356 +/- 3 nm, whereas for the basic form it is at 380 +/- 3 nm. The apparent pK of the bound coumarine derivative is 7.45 +/- 0.30. The bias and the precision for pO(2) determinations in blood samples are about - 1 and +/- 1.5 torr, respectively. For pH determinations, the respective values are about 0.02 and 0.04 pH units and for pCO(2) about 1 and 2.5 torr. The sensors described are suited for production on an industrial scale.