Analytical Sciences

Simultaneous Determination of Rhodium and Iridium Using Derivative Spectrophotometry after Preconcentration of Their 2-(5-Bromo-2-pyridylazo)-5-diethylaminophenol Chelates onto Microcrystalline Naphthalene

Joseph Patrick PANCRAS and Bal Krishan PURI *

Department of Chemistry, Indian Institute of Technology, Delhi, Hauz Khas, New Delhi-110016, India

Rhodium and iridium were preconcentrated from a fairly large volume of their aqueous solutions using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) and tetraphenylborate onto microcrystalline naphthalene in the pH ranges 5.0 - 6.5 and 3.5 - 5.5, respectively. The solid mass obtained after filtration was dissolved in 5 ml of dimethylformamide (DMF). A derivative spectrophotometric method using a zero-crossing technique measurement is described for their simultaneous determination in mixtures. The determination of rhodium and iridium in the concentration ranges 0.15 - 12.5 and 0.25 - 10.0 mg in 5 ml of the final DMF solutions, respectively, shows good linearity in the calibration plots. The detection limits are 72 ng and 133 ng for rhodium and iridium, respectively. Favorable selectivity in the presence of common ions was achieved by adding EDTA after complex formation. Various parameters were studied in order to optimize the conditions for the simultaneous determination of rhodium and iridium in various synthetic samples corresponding to their standard alloys. (Keywords: Rhodium, iridium, derivative spectrophotometry, simultaneous determination, 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol, synthetic samples, tetraphenylborate)

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