Spectrophotometric determination ofrhodium(III) using 5-Br-PADAP and N-hydroxy-N ,N' -diphenylbenzamidine as reagent by extracting it in dichloromethane

School of Studies in Chemistry, Pt. Ravishankar Shukla University. Raipur-492 010, India

E-mail : debmanas@yahoo.com

Manuscript received 13 July 2004, revised 14 December 2004, accepted 19 January 2005

A rapid and sensitive spectrophotometric method for the determination of Rh^III with 2-[(5-bromo-2-pyridylazo)]-5-diethylaminophenol (5-Br-PADAP) is describcd. The Rh^III -2-[(5-bromo-2-pyridylazo)]-5-diethylaminophcnol (5-Br-PADAP) complex is extracted with N-hydroxy-N,N'-diphenylbenzamidine (HDPBA) in dichloromethanc at pH range 5.8-6.5 to give a red coloured complex. The extracted complex shows λ_max at 460 nm. The reproducibility of the method is checked by finding relative standard deviation value (RSD, n = 10) for solution containing 1 µg ml^-1 Rh^III, and the RSD value of the method is found to be 1.7%. The system obeyed Beer's law up to 0.6 µg ml^-1 of rhodium and the detection limit of the method is 32 ng ml^-1 on a three times the standard deviation of the blank absorbance basis. The Sandell's sensitivity and molar absorptivity of the complex are 0.00036 µg ml¹ and 2.8 x 10⁵ dm³ mol^-1 cm^-1, respectively. The effect of foreign ions and other experimental variables are studied. Rh^III has been successfully determined in automobile exhaust sample, soil and vegetation samples.