Dedicated ionization chamber (IC) was built and installed to measure the energy loss of very heavy nuclei at 2.7 MeV/ u produced in fusion reactions in inverse kinematics (beam of 208Pb). After going through the IC, products of reactions on 12C, 18O targets are implanted in a Si detector. Their identification through their α-decay chain is ambiguous when their half-life is short. After calibration with Pb and Th nuclei, the IC signal allowed us to resolve these ambiguities. In the search for rare super-heavy nuclei produced in fusion reactions in inverse or symmetric kinematics, such a chamber will provide direct information on the nuclear charge of each implanted nucleus.