A system for collecting nitrous oxide in exhalation air and subsequently delivering the nitrous oxide to further processing which comprises a number of mutually replaceable adsorption units (201). Every unit has a nitrous oxide reversible adsorbent (213a) and: i) an inlet port (214a) and an outlet port (214b) for exhalation air, ii) an inlet port (215a) and an outlet port (215b) for desorbing gas, together with A) a docking arrangement (202) which is associated with adsorption of nitrous oxide and used for connecting a face mask (204) to the inlet port (214a), and B) a docking arrangement (203) which is associated with desorption of nitrous oxide and used for connecting the outlet port (215b) to further processing of nitrous oxide. Another aspect is an adsorption unit (201,301,401) unit as defined in the preceding paragraph which is capable of being regenerated by passing a desorbing gas through the adsorbent.
