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

3-(5'-tetrazolylazo)-2,6-Diaminotoluene (TEADAT, H3L2+) 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) l . mol-1. cm-1 at 536 nm. Equilibrium constants beta( nl) for reactions PdCl42- + nH3L2+ half arrow right over half arrow l eft PdCl4-n(H2L)n2n-2 + n Cl- + n H+ were determined: log beta1 = 4.0 9 +/- 0.05, log beta2 = 8.40 +/- 0.02, corresponding stability condit ional constants of PdCl3(H2L) and PdCl2(H2L)2(2+) were log beta1 = 19. 03, log beta2 = 26.74. The formation of complexes was rather slow but could be speeded up considerably by the catalytic effect of trace amou nts of thiocyanate. Constant absorbance values were thus reached in 2- 5 min. A rapid, sensitive and highly specific method for the determina tion of palladium(II) at pH 1.42 in 0.25M NaCl has been worked out wit h a detection limit of 0.54 mug. Interference of precious and common m etal ions have been studied and the method has been applied for the de termination of palladium in Pd asbestos, oakay alloys and various cata lysts and for the determination of palladium in precious metals.