Abstract
Summary A sensitive spectrophotometric method for the determination of rhodium is based upon the purple color (absorbance maximum at 565 mμ) produced by sym-diphenylcarbazone at p h 3.0; methanol and N,N-dimethylformamide are used as solvents. For measurement in a 1-cm cell, the optimum range is about 0.3 to 1.5 p.p.m., and the useful lower limit is about 0.05 p.p.m. Although careful regulation of p h is required, the other variables are not critical. Preparation of the sample requires fuming down nearly to dryness with perchloric acid; by this procedure chloride and nitrate are removed, osmium and ruthenium are completely volatilized as tetroxides, and platinum and gold are completely precipitated. Iridium, which forms a purple product with the reagent, also interferes on account of the low p h at which it precipitates as hydrous oxide. Interference from chromium(VI) and mercury(II) can be removed by volatilizing chromyl chloride and mercury(II) chloride, respectively. Copper(II) must be absent. The purple rhodium product is not retained on either cation- or anion-exchange resins. The method of continuous variations indicates a reaction ratio of 2 moles of sym-diphenylcarbazone to 1 mole of rhodium.
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