Simultaneous determination of rhodium and palladium by spectrophotometry with 5-(5-nitor-2- pyridylazo)-5-dimethylaminoamiline

A novel method for the simultaneous spectrophotometric determination of rhodium and palladium based on the colour reaction of rhodium and palladium with 5 (5 nitor 2 pyridylazo) 5 dimethylaminoamiline (5 NO 2 PADMA) was proposed. The results showed that rhodium reacted with 5 NO 2 PADMA in the pH range of 3.5～7 0 to form a red complex which could be further changed into another deep coloured stable species by addition of mineral acid. Palladium formed a blue complex with the reagent in a strong acidic medium. The apparent molar absorptivity of the rhodium and palladium complexes were 1 39×10 5 and 9 4×10 4 L·mol -1 ·cm -1 at 620 nm,respectively. Berr's law was obeyed in the range of 0～0.56 μg·mL -1 for Rh and 0～1.4 μg·mL -1 for Pd. Most common ions did not interfere. The method was applied to the determination of rhodium and palladium in ore and catalyst samples with satisfatory results.