4-(2-Quinolylazo)phenol as a Spectrophotometric Reagent for Palladium(II), Osmium(VIII), and Gold(III)

Abstract

Reaction behavior of 4-(2-quinolylazo)phenol (p-QAP) is established with three noble metals, i.e. palladium(II), osmium(VIII), and gold(III), under various conditions. Palladium(II) forms a 1:1 greenish violet complex at pH 8–10 (absorption maximum at 580 nm), while osmium(VIII) forms a 1:1 violet compex at pH 8–9.5 (absorption maximum at 550 nm) with the ethanolic solution of p-QAP. Color reaction with gold(III) with ethanolic solution of p-QAP is instantaneous, but fades away with time. However, a 4:4:2 mixture of water, ethanol, and cyclohexanol stabilizes this color for 45 min. Thus a 1:1 red gold(III) complex formed at pH 8–9.5 absorbs maximum at 550 nm. The Sandell’s sensitivities (ng cm−2) of the color reactions are 2.7, 3.9, and 9.8 with palladium(II), osmium(VIII), and gold(III) respectively. Other physicochemical characteristics of the complexes are established. A number of foreign ions tested for their interferences and use of masking agents wherever necessaty it tabulated. Synthetic solutions identical in composition to some palladium(II) and gold(III) alloys are estimated to ascertain the suitability of the reagent.

Development of a selective and sensitive colour reagent for gold and silver ions and its application to desktop scanner analysis

“…However, conventional spectrophotometry stands out as a relatively low cost, simple and easy-to-use technique. The spectrophotometric determination of silver is usually achieved using its reaction with dithizone, 15 4-(2-quinolylazo)phenol ( p -QAP), 16 4,4′-bis(dimethylamino)thiobenzophenone, 17 2-cyano-3-iminodithiobutyrate (CIDT), 18 or 2′,3′-dihydroxypyridyl-4′-azobenzene-4-arsonate (DHP-4A); 19 however, that of gold is achieved using dithizone, 20 4-(2-pyridylazo)resorcinol (PAR), 21 4-(2-thiazolylazo)resorcinol (TAR), 22 methiomeprazine hydrochloride (MMH), 23 4-(2-quinolylazo)phenol ( p -QAP), 24 or dithiodiantipyrylmethane. 25 Nevertheless, the poor selectivity, sensitivity and/or precision restrains the use of most of these reagents.…”

Spectrophotometric and derivative spectrophotometric determination of palladium(II) using pyridopyridazine dithione in the presence of non-ionic surfactant

“…Numerous spectrophotometric methods are available for the determination of palladium [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17], but most have low sensitivity [2][3][4][5][6][7], are nonselective [6][7][8][9] and are based on solvent extraction [10][11][12][13][14][15][16][17]. Moreover, the determination of palladium in the presence of noble metals without preliminary extraction or use of masking agent is difficult, because the spectra of the * To whom correspondence should be addressed respective complexes with the chromogenic reagent tend to overlap [14][15][16][17].…”