Kin-Tek Laboratories (La Marque, TX) offers permeation tubes used in detection systems. Dopant tubes continuously dispense a small flow of a reagent vapor used to enhance response to specific substances. The basic dopant tube is a small plastic cylinder with the pure dopant compound sealed inside. Dopant vapor leaks slowly (and continuously) into the detection system sample stream where it reacts to enhance detection of the target compound.
Check out www.kin-tek.com to learn more.