Plasmochin(N-diethylamine-iaopentyl-8-amino-6-methoxyquinoline) in the presence of 0.1N perchloric acid and 8% oxalic acid, reacts with CrO^-2₄(or Cr₂O7^-2₇) ions to give a red-violet coloration which is not extracted by ordinary organic solvents.The limit of identification is 0.06'Y at a dilution Limit of 1:10⁶, Ce⁺⁴, Au⁺³, VO^-₃, Br^-₃, IO^-₃, I0^-₄ and NO^-₂ ions interfere with the detectors of CrO^-2₄ ions.The limit of proportion of CrO^-2₄ ion with 74 ions has been determined and in most cases, they neither affect the reaction nor decrease the eenaitivity even in the ratio of 1:200.