Determination of a trace amount of palladium by dual-wavelength overlapping spectrophotometry

A novel method for the determination of trace amount of palladium with 5-(5-iodine-2-pyridylazo)-2,4-diaminotoluene(5-I-PADAT) by dual-wavelength overlapping spectrophotometry was developed.The experimental results show that,in the medium of 0.6~2.4 mol/L HClO4,Pd reacts with 5-I-PADAT to form a stable blue-purple complex with two absorption peaks at 584 nm and 546 nm,respectively,and the sum of absorbance at these two peaks shows good linearity with Pd concentration.The apparent molar absorptivity is 1.18×105 L·mol-1·cm-1,1.6 times higher than that of single-wavelength spectrophotometry.Beer's law is obeyed in the range of 0~1.2 μg/mL for palladium.Relatively large amounts of co-existing elements,including other precious metal ions can be tolerated.The method is simple,highly sensitive and selective.It can be used to determine a trace amount of Pd in molecular sieves with satisfactory results.