Spectrophotometric determination of palladium(II) with four water-soluble heterocyclic azo dyes

Abstract

1-(Tetrazolylazo)-2-hydroxynaphthalene-3,6-disulphonic acid (T-azo-R), 2-(tetrazolylazo)-1,8-dihydroxynaphthalene-3,6-disulphonic acid (T-azo-C), 1-(thiazolylazo)-2-hydroxynaphthalene-3,6-disulphonic acid (3,6-disulpho-TAN) and 2-(thiazolylazo)-1,8-dihydroxynaphthalene-3,6-disulphonic acid (TAAC) have been investigated as spectrophotometric reagents for palladium(II). Stable water-soluble complexes are formed, even in 1 M perchloric acid, and at this acidity the considered reagents are specific for palladium(II). A number of donor anions interfere in the palladium(II) determination, mainly by competing with the azo dyes for complexation with the metal ion. The first three reagents were found to form 1:1 (metal to ligand) complexes, while the last forms a 1:2 complex, with a molar absorptivity more than twice that of the others. In all instances the spectra of the complexes are well resolved with respect to those of the free ligands. Concentrations of palladium(II) ranging from 2 × 10^–6 to 1.5 × 10^–4M can be determined spectrophotometrically. The accuracy (relative difference between the known and the found concentration) is 1% at a concentration of 2 × 10^–5M.