Third derivative spectrophotometric determination of trace rhodium after pre-concentration with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol chelate/tetraphenylborate ion pair on microcrystalline naphthalene

Abstract

Rhodium is quantitatively retained with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol(5-Br-PADAP)-tetraphenylborate(TPB) on microcrystalline naphthalene in the pH range 3.3–5.8 from a large volume of aqueous solutions of various synthetic samples. After filtration, the solid mass consisting of the rhodium complex–ion pair and naphthalene was dissolved in 5 ml of dimethylformamide and rhodium was determined by third derivative spectrophotometry. The detection limit is 20 ng ml −1 (signal-to-noise ratio = 2), and the calibration graph is linear for 40–7500 ng ml −1 Rh in dimethylformamide solution with a correlation coefficient of 0.9997 ( n = 6). Eight replicate determinations of 5 μg of rhodium in 5 ml of dimethylformamide solution gave a mean signal (peak to peak signal between λ 1 and λ 2) of 0.768 with a relative standard deviation of 1.2% ( n = 6). The sensitivity of the method is 0.756 (d 3A/dnm 3)ml μg −1 found from the calibration slope. The interference of a large number of anions and cations has been studied. The cationic interferences may be masked with EDTA. The optimized conditions developed were utilized for the trace determination of rhodium in various synthetic samples.