Hemoglobin test for neutral atmosphere
Mix with pH 7.4 buffer to make a hemoglobin solution in the flask.
Make the unit air-tight and purge it with nitrogen to make it inert. (Will require freeze-pump-thaw method to also purge the buffer solution of dissolved oxygen as that will ruin this indicator)
Once everything is inert, introduce a 0.1 M Sodium Dithionite solution via syringe. This will reduce the iron center from Fe3+ to Fe2+. Hemoglobin cannot bind oxygen in its 3+ state but binds it extremely fast in a 2+ state. When it binds oxygen, the solution goes from a pale yellow to a distinct blood-red.
For the Metal Head chemists and anarchists out there.