[en] This paper discusses the development of a separation method for isolation of "1"7"1Tm from a half-gram irradiated erbium target in support of stockpile stewardship and astrophysics research. The developed procedure is based on cation exchange separation using alpha-hydroxyisobutyric acid (α-HIBA) as chelating agent. It is able to achieve either a decontamination factor of 1.4(4) × 10"5 with 68.9(3) % recovery or 95.4(3) % recovery with a decontamination factor of 5.82(7) × 10"3 for a mock 500-mg target containing 17.9 mg thulium in a single pass-through at room temperature. (author)