  The ALICE Collaboration is planning a major upgrade of its central barrel
detectors to be able to cope with the increased LHC luminosity beyond 2020. For
the TPC, this implies a replacement of the currently used gated MWPCs
(Multi-Wire Proportional Chamber) by GEM (Gas Electron Multiplier) based
readout chambers. In order to prove, that the present particle identification
capabilities via measurement of the specific energy loss are retained after the
upgrade, a prototype of the ALICE IROC (Inner Readout Chamber) has been
evaluated in a test beam campaign at the CERN PS. The d$E$/d$x$ resolution of
the prototype has been proven to be fully compatible with the current MWPCs.
