Highly specific spectrophotometric method for palladium(II) determination with 3-(5'-tetrazolylazo)-2,6-Diaminotoluene in the presence of chlorides. Kinetic and equilibrium study of reactions

Our plain-English summary of Highly specific spectrophotometric method for palladium(II) determination with 3-(5'-tetrazolylazo)-2,6-Diaminotoluene in the presence of chlorides. Kinetic and equilibrium study of reactions, by O. Hernández, A.I. Jiménez, F. Jiménez, et al (Talanta, 1994).

The study

• Authors: O. Hernández, A.I. Jiménez, F. Jiménez, J.J. Arias, J. Havel
• Journal: Talanta
• Published: 1994;41(5):775-82
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

3-(5'-tetrazolylazo)-2,6-Diaminotoluene (TEADAT, H(3)L(2+)) forms stable 1:1 and 1:2 (metal:ligand) pink-red complexes (lambda(max) 506 and 536 nm) with palladium(II). The apparent molar absorptivity of 1:2 complex is 5.2 x 10(4) 1.mol(-1). cm(-1) at 536 nm. Equilibrium constants beta*(nl) for reactions PdCl(2-)(4) + nH(3)L(2+) right harpoon over left harpoonright harpoon over left harpoon PdCl(4-n) (H(2)L)(2n-2)(n) + n Cl(-) + n H(+) were determined: logbeta*(1) = 4.09 +/- 0.05, logbeta*(2) = 8.40 +/- 0.02, corresponding stability conditional constants of PdCl(3)(H(2)L) and PdCl(2)(H(2)L)(2+)(2) were log beta(1) = 19.03, log beta(2) = 26.74. The formation of complexes was rather slow but could be speeded up considerably by the catalytic effect of trace amounts of thiocyanate. Constant absorbance values were thus reached in 2-5 min. A rapid, sensitive and highly specific method for the determination of palladium(II) at pH 1.42 in 0.25M NACl has been worked out with a detection limit of 0.54 mug. Interference of precious and common metal ions have been studied and the method has been applied for the determination of palladium in Pd asbestos, oakay alloys and various catalysts and for the determination of palladium in precious metals.

In plain English

This laboratory chemistry study did not examine asbestos exposure or health. The authors synthesized a color-forming reagent called TEADAT and developed a method for measuring the metal palladium with it in a sodium chloride solution. Palladium and the reagent formed two colored complexes, one with one reagent molecule and one with two. Without help, the reaction took about 20 to 60 minutes to reach equilibrium. Adding trace amounts of thiocyanate gave steady readings after 2 to 5 minutes. The detection limit was 0.54 micrograms of palladium. Excesses of many other metal ions did not interfere, and silver interference could be removed with chloride. On nine synthetic metal mixtures, the average relative error was 2.57%. Asbestos appeared only as the support material in one of five commercial palladium catalysts tested. For this "Pd-asbestos" catalyst, the method found 4.32% palladium, compared with 4.38% by atomic absorption spectroscopy (AAS). The authors concluded that the method is simple, highly sensitive and free from interference by a large number of elements, particularly the other platinum group metals.

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What the study did and found

• Design: Laboratory analytical chemistry study: development of a spectrophotometric (color-measurement) method for palladium, with equilibrium and kinetic analysis of the reactions
• Who was studied: No people or animals were studied. The method was tested on nine synthetic mixtures matching the composition of some alloys and on five commercial (Fluka) hydrogenation catalysts, one of them palladium on asbestos.
• Exposure: Not applicable: no asbestos exposure was studied. Asbestos appears only as the support material of one commercial palladium catalyst (Pd-asbestos) that was analyzed for its palladium content. No fiber type is named.
• Main results:
  • Palladium formed 1:1 and 1:2 (metal:reagent) complexes with TEADAT. The recommended equilibrium constants were log beta*1 = 4.09 plus or minus 0.05 and log beta*2 = 8.40 plus or minus 0.02.
  • Without thiocyanate, the reaction reached equilibrium in about 20-60 min. With small concentrations of thiocyanate, constant absorbance values were obtained after 2-5 min.
  • Under optimal conditions, Beer's law was obeyed from 0.02 to 2.00 micrograms per ml palladium, with an apparent molar absorptivity of 52,000 l per mol per cm.
  • The detection limit was 0.54 micrograms. The relative error for determining 30 micrograms of palladium was 2.6%.
  • None of the precious metal ions tested interfered. Silver interference was eliminated with 1M chloride as a masking agent.
  • In nine synthetic mixtures matching some alloys, the average relative error was 2.57% (each result the mean of three determinations).
  • For the Pd-asbestos hydrogenation catalyst, palladium found was 4.38% by AAS and 4.32% by the proposed method (mean of three determinations).
• The authors' conclusion: The authors concluded that the method is very simple, highly sensitive and free from interference by a large number of elements, particularly the other platinum group metals, and that the reagent is specific for palladium(II).
• Limitations the authors state:
  • The pH readings were not corrected for ionic strength, salt concentration or ethanol, so the authors say the pH values should be considered conditional.
  • Stability constants calculated from the kinetic data may be lower than those from the equilibrium analysis because the ionic strength differed between the two experiments.

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