Effects of masking agents on the separation of copper(II) from iron(III) by continuous solvent extraction with 8-hydroxyquinoline.

metal complexes, but is useful in the case of metal complexes with low extractability. This process has thus been applied to the separation of metals, which is difficult by conventional batch extraction.1 Extraction reagents (HR) are usually consumed in amounts several hundred times those of metals (M). Complexes to be extractable into an organic solvent {MRn·(HR)m} are not always obtained using diluted extraction reagents. Frequently, unextractable MRn·(H2O)y are formed at low concentrations of the extraction reagent. At low concentrations of extraction reagents, M and N as metal ions form different structures {MRn(HR)m, NRn(H2O)y}, so that their extractability differs significantly from each other. Even if their extractability decreases, separation may be achieved by continuous extraction. The separation of nickel(II) from cobalt(II) with 8hydroxyquinoline (8-quinolinol) is such an example.2 The selectivity of extraction with chelating reagents is enhanced by masking agents, which suppress the extraction of interfering ions without suppressing the analytes. Because masking agents generally interfere with the extraction of analytes and coexisting ions, useful masking agents are few in number. In the case of continuous extraction, masking agents may be used to separate metal ions, even though they suppress the extractability, provided differences in the extractability of metal complexes are large. Even if the extractability of the analyte by a conventional batch method decreases from 100% to 50% due to a masking agent, separation by continuous extraction may be effective at the extractability of coexisting ions at less than 0.1%. Optimum masking agents were sought so as to separate metals by continuous extraction. The effects of masking agents on the separation of copper(II) from iron(III) with 8hydroxyquinoline (a well-known chelating reagent) were examined. The separation of these metals is difficult by a conventional batch method using 8-hydroxyquinoline.