Have you looked at Dräger tubes? Dräger Tubes are glass vials filled with a chemical reagent that reacts to a specific chemical or family of
chemicals. A calibrated 100 ml sample of air is drawn through the tube. If the targeted chemical(s) is present the reagent in the tube changes color
and the length of the color change typically indicates the measured concentration. They are a bit pricey for the hobbyist.
https://www.gasdetectionwarehouse.com/draeger-gas-detector-t... |