During 1989 and 1990 over 180 000 hadronic and leptonic events, corresponding to 8 pb−1 of luminosity, were collected by the ALEPH detector in a scan of the Z peak at the e+e− collider LEP. This letter reports the results of a search in these data for particles with unexpected mass and charge by measurement of the ionization energy loss of charged tracks in the ALEPH TPC central tracking detector. The mass limits for the pair production of fractionally charged particles and of heavy, long lived charged particles are extended to 43 GeV/c2 at 90% confidence level. If single production of a heavy particle is considered, the mass limit is extended to more than 70 GeV/c2.