  The CMS RPC muon detector utilizes a gas recirculation system called closed
loop (CL) to cope with large gas mixture volumes and costs. A systematic study
of CL gas purifiers has been carried out over 400 days between July 2008 and
August 2009 at CERN in a low-radiation test area, with the use of RPC chambers
with currents monitoring, and gas analysis sampling points. The study aimed to
fully clarify the presence of pollutants, the chemistry of purifiers used in
the CL, and the regeneration procedure. Preliminary results on contaminants
release and purifier characterization are reported.
