Kinetic spectrophotometric determination of trace rhodium with oxidation of amaranth by potassium periodate

A new catalytic spectrophotometric method for the determination of trace rhodium was established based on its catalytic effect on the oxidation of the amaranth(4-sulfo-1-naphthylazo-2-naphthol-3,6-disulfonic trisodium) by KIO4 in H3PO4 medium and hot-water bath.A linear relationship was obtained between the reaction rate and the concentration of Rh(Ⅲ) in the range of 0-0.10μg/mL.The detection limit was 7.0×10-3μg/mL.The relative standard deviation for the detection of 0.04μg/mL Rh(Ⅲ) is 2.5%(n=10).The apparent activation energy of the catalytic reaction is 81.36kJ/mol.The effects of more than 20 kinds of foreign ions were tested and the interference from many common ions could be tolerated.The method has been applied to the determination of trace rhodium in the Rh-Al catalysts with the RSD of 1.4-1.6% and the recovery of 96-103%.