[Determination of microamounts of palladium by triple-wavelength overlapping spectrophotometry]

The method for the determination of microamounts of palladium with 2-(3,5-dichlolor-2-pyridylazo)-5-dimethylaminoaniline (3,5-diCl-PADMA) by triple-wavelength overlapping spectrophotometry has been developed. It's shown that in the medium of 0.02-1.6 mol x L(-1) H2SO4, Pd reacts with 3,5-diCl-PADMA to form a stable 1:1 green-blue complex, which has two different positive absorption peaks and one negative absorption peak at 621 nm, 574 nm and 434 nm respectively, and their absorbance sum showed good linearity with Pd concentration. The apparent molar absorptivity is 2.03 x 10(5) L x mol(-1) x cm(-1), which is twice as high as that of single-wavelength spectrophotometry. Beer's law is obeyed in the range of 0-1.2 mg x L(-1) 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, and has been used to the determination of microamounts of Pd in ore, alloy and molecular sieve with satisfactory results.