A NOVEL OXYGEN AND/OR CARBON DIOXIDE-SENSITIVE OPTICAL TRANSDUCER

A novel oxygen (O-2) and/or carbon dioxide (CO2)-sensitive transducer for the measurement of both gaseous O-2 and CO2 over the concentration ranges of O-2, 0-100% and CO2, 0-10% has been described employing a solution of 10.6 mu M fluorescein (FL) and 190 mu M potassium hydroxide in a solvent mixtures of 1:1 (v/v) N,N'-diethylaniline (DEA) and N,N-dimethylformamide. Increasing O-2 concentrations cause the absorbance of the solution at a wavelength of 400 nm to increase owing to a contact charge transfer reaction existing between O-2 and DEA molecules, and increasing CO2 concentrations produce a non-linear fall in absorbance at 520 nm as the colour of FL changes from its orange dianion form to the colourless neutral, lactonic form. Both processes are independent of each other and reversible. The response to changes in O-2 concentrations is in good agreement with Beer-Lambert's law and the response to changes in CO2 concentrations in non-linear. A fibre optic sensing system based on this solvent-dye solution has been set up for continuous and reversible determination of both gaseous O-2 and CO2. Possible applications include environmental and physiological monitoring of O-2 over the ranges of 0-100% and CO2, 0-10%.