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LEE TE-FUNG, WANG NAI-CHING and SHEN NAI-KUEI (Department of Chemistry, First and Second Medical Colleges of Shanghai)  
Plasmochin (N-diethylamine-isopentyl-8-amino-6-methoxyquinoline) in thepresence of 0.1N perchloric acid and 8% oxalic acid, reacts with Cr0_4~(-2) (orCr_2O_7~(-2)) ions to give a red-violet coloration which is not extracted by ordinaryorganic solvents. The limit of identification is 0.05γ at a dilution limit of 1: 10~6,Ge~(+4), Au~(+3), VO_3~-, BrO_3~-, IO_3~-, IO_4~- and NO_2~- ions interfere with the detecton of CrO_4~(-2)ions. The limit of proportion of CrO_4~(-2) ion with 74 ions has been determined andin most cases, they neither affect the reaction nor decrease the sensitivity evenin the ratio of 1: 200. Among the interfering ions Ce~(+4) and An~(+3) can be separated by ammoniumhydroxide and VO_3~- by oxine-chloroform extraction. The results after separation issatisfactory. And in a mixture of ions containing Ce~(+4) Au~(+3), VO_3~- and Cr~(+3) with aproportion limit of 20: 20: 20: 1, Cr~(+3) ion (0.094γ/0.05ml) can still be detected. Chro-mium should be previously oxidized in the sulfuric acid solution by ammoniumpersulfate or in the alkaline solution by hydrogen peroxide before the seperationof interfering ions. Plasmochin is a good reagent for detection Of CrO_4~(-3) ion owing to its high sta-bility and high sensitivity and selectivity of the reaction.
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