Just a suggestion, a dilute gold cyanide aqueous solution homogeneous catalyst at room temperature will reacts CO + O2 to form carbon dioxide. Then you can detect the CO2 with IR spectroscopy. So any O2 would react with CO producing a well characterized CO2 molecule using a well known spectroscopy technique. Section 2.11. I think as little as 0.001M solution would likely do it. Article Unified Explanation of Catalyzed and Non-Catalyzed Chemical Reactions