A simple apparatus is used for the separation of the components of a mixture of CO, H2, and CH4. The separation of CO and CH4 by selective oxidation with CuO was studied with 14CH4. The 13C isotope fractionation during the oxidation of CO with I2O5 and with CuO, and during the elevated temperature oxidation of CH4 with CuO, and the tritium fraction during the oxidation of tritiated hydrogen with CuO are reported.