Method and Apparatus for separating at least one CO isotope compound, especially isotope compound 13C16O, from natural CO, comprising: a rectification column system (110) comprising a plurality of rectification sections (112,114,116,118,120) arranged adjacent to one another in a chain-like manner, including an upper rectification section (112) and a plurality of lower rectification sections (114,116,118,120), each rectification section comprising a heating means (112a,114a,116a,118a,120a) to maintain evaporation of liquid present therein, provided that the heating means (112a) of the at least one of the plurality of rectification sections (112) is provided to comprise a heat pump cycle (112b).