Apparatus and method in which a beam of radiant energy (16) is passed into a medium at a wavelength selected to cause a response of an analyte in the medium or of a sensor (10,14) exposed to the medium, the sensor comprising a reagent whose optical properties change in response to the presence of the...http://www.google.se/patents/US5212099?utm_source=gb-gplus-sharePatent US5212099 - Method and apparatus for optically measuring concentration of an analyte
