Spectrophotometric determination of micro Ruthenium(II) using 5-(5-Iodine-2pyridylazo)-2,4-diaminotoluene

A new reagent 5-(5-Iodine-2-pyridylazo)-2,4-diaminotoluene(5-I-PADAT) was recommended for the determination of ruthenium(Ⅱ).It was shown that in aqueous 30% ethanol solution at pH 4.0～6.2 ruthenium(Ⅱ) reacts with 5-I-PADAT to form a stable complex showing a maximum absorption at 584 nm.The complex can be changed into another species possessing higher absorption characteristics by the addition of a mineral acid(e.g.HCl,H2SO4,HClO4,H3PO4).The optimal concentration of HCl,H2SO4,HClO4 or H3PO4 is found to be 0.15～0.60 mol/L,0.15～0.48 mol/L,0.15～0.48 mol/L and 0.15～0.90 mol/L respectively.The apparent molar absorptivity is 5.72×104 L·mol-1·cm-1 at 509 nm.Beer′s law is obeyed in the range of 0～0.5 μg/mL.The precious metal ions,such as Ag(I) in 40 times,Os(Ⅲ) in 10 times,Au(Ⅲ) in 6 times,and Pt(IV),Rh(Ⅲ) and Ir(Ⅲ) in 4 times do not interfere the determination of ruthenium.The interference of palladium can be eliminated by taking advantage of the differences of reaction temperature and acidity between palladium(Ⅱ) and ruthenium(Ⅱ) with 5-I-PADAT.The method has good selectivity.It has been successfully applied to the determination of micro ruthenium in catalysts with satisfactory results.