Abstract: A method and apparatus are described for an accurate determination of the concentration of a gas, vapor or a gas dissolved in a sample which compensate for variations in temperature and light - source intensity. The apparatus comprises a sensor containing a fluorescent reagent connected to a transfer optic, such as fiber optics prism or glas pipes, and to a reference sensor containing the same fluorescent reagent. The reference sensor is encapsulated in an environment containing air. The light emitted from the first sensor and the reference sensor is determined and recorded automatically, the concentration of the gas being calculated based on the output from said light detectors using calibration data of the fluorescent reagent present in the sensors. The reagent is immobilized in the sensor by a glue, such as a silicon glue.

Abstract: A method for the manufacture of an improved sensor element for determining the amount of oxygen in a sample, comprises the steps of: (a) mixing a fluorescent reagent with a silicone oil which has a molecular weight of 6,700 to 80,000 and most preferably in the range of between 15,000 and 30,000; (b) heating the mixture at a temperature in the range of between 150.degree. to 350.degree. C. and (c) adding an optical insulating material forming an optical insulating layer onto the fluorescent reagent. Optionally, a crosslinking agent is incorporated. In order to increase the efficiency of fluorescence, an additionally layer of light scattering material is inserted between the fluorescent reagent layer and that of the insulator.