Selective stopped-flow injection spectrophotometric determination of palladium(II) in hydrogenation and automobile exhaust gas converter catalysts

A stopped-flow injection spectrophotometric method is reported for the dete rmination of palladium(II), using 2,2'-dipyridy-2-pyridylhydrazone (DPPH) a s a colour forming reagent. The absorbance of the Pd(II)-DPPH complex was m onitored at 540 nm, at pH approximate to 0.3. The various chemical and phys ical parameters were optimized and a study of interfering ions was also car ried out. The calibration graph has two linear parts, first in the range 0- 25 mg l(-1) (s(r)=0.44%, r=0.9999) with a detection limit of c(L)=0.084 mg l(-1) and the second in the range 25-60 mg l(-1) (s(r)=1.6%, r=0.9996). In both cases the sampling rate was 30 injections per hour. The method is very selective because the strongly acidic medium used prevented the formation of complexes of the reagent with other ions. The method was successfully ap plied to the determination of palladium in hydrogenation and automobile exh aust gas converters catalysts. The relative standard deviation of the mean values and the recovery ranged between 0.6 and 1.6% and 97.0-102.6%, respec tively. (C) 2000 Elsevier Science B.V. All rights reserved.