Application of [(2-Hydroxybenzaldehyde)-3-Isatin]-Bishydrazone to the Photometric Determination of Palladium(II) in a Nickel Anode Material

A new complexing analytical reagent is synthesized by the condensation of salicylic aldehyde with isatin hydrazone. The dissociation constant of the reagent pK = 9.48 ± 0.03 is determined. The structure of the reagent is studied by X-ray diffraction and NMR spectroscopy. The complexation of palladium(II) with [(2-hydroxybenzaldehyde)-3-isatin]-bishydrazone (R) in the presence and absence of diantipyrylmethane (DAM), 8-hydroxyquinoline (8-HQ), and diphenylguanidine (DPG) is studied by spectrophotometry. Optimum conditions for complexation (λopt, pHopt) are selected. It is found that palladium(II) forms colored mixed-ligand complexes with the reagent in the presence of the third component, DAM, 8-HQ, or DPG. The Pd(II)–R complex exhibits the maximum absorbance at the wavelength 440 nm, and the Pd(II)–R–DAM, Pd(II)–R–8-HQ, and Pd(II)–R–DPG complexes, at 465, 490, and 450 nm, respectively. The molar absorption coefficients for Pd(II)–R are 6000 L/(mol cm), and for Pd(II)–R–DAM, Pd(II)–R–8-HQ, and Pd(II)–R–DPG they are 10 000, 8000, and 7500 L/(mol cm), respectively. The optimum pH value for Pd(II)–R is 4, for Pd(II)–R–DAM and Pd(II)–R–DPG it is 2, and for Pd(II)–R–8-HQ it is 3. The stability constants of the complexes are determined. The region of adherence to the Beer law is found. The equations of the calibration graphs are constructed using the least-squares technique. The ratio of components in the composition of homogeneous and mixed-ligand complexes is determined by the methods of isomolar series, continuous variations (Job’s method), and slope. All methods show that the ratio of the Pd(II)–R components in the binary complex is 1 : 2, and in the mixed-ligand complexes Pd(II)–R–8-HQ and Pd(II)–R–DPG – 1 : 1 : 1, Pd(II)–R–DAM – 1 : 2 : 1. The effect of some foreign ions and masking substances on the formation of homogeneous and mixed-ligand complexes of palladium(II) is studied. It is found that Na(I), K(I), Ca(II), Ba(II), Cd(II), Ni(II), Cr (III), Co(II), Pd(IV), platinum-group metals, and many anions do not interfere with the determination of Pd(II). The developed procedure is applied to the determination of trace amounts of palladium(II) in a nickel anode material.