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 determination of palladium(II), using 2,2'-dipyridy-2-pyridylhydrazone (DPPH) as a colour forming reagent. The absorbance of the Pd(II)-DPPH complex was monitored at 540 nm, at pH approximate to 0.3. The various chemical and physical parameters were optimized and a study of interfering ions was also carried 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 applied to the determination of palladium in hydrogenation and automobile exhaust 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%, respectively. (C) 2000 Elsevier Science B.V. All rights reserved.