Spectrophotometric determination of silver and gold with 5-(2,4-dihydroxybenzylidene)rhodanine and cationic surfactants

Abstract

The synthesis, characteristics and analytical reactions of 5-(2,4-dihydroxybenzylidene)rhodanine (2,4-DHBR) with silver and gold are described. Maximum enhancement of the absorbance of the chelates is obtained in the presence of the cationic surfactants cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPB), respectively. Each metal ion forms two ternary complexes depending on 2,4-DHBR concentration. The stoichiometries of the complexes are 1:1:1 and 1:2:3 (Ag–2,4-DHBR–CTAB) and 1:2:3 and 1:3:4(Au–2,4-DHBR–CPB). The complexes with higher reagent/metal ratio were used for the spectrophotometric determination of silver and gold. In the pH ranges 9.2–10.6 and 9.3–10.8, the molar absorptivities are 7.11 × 10⁴(Ag) and 8.45 × 10⁴(Au) dm³ mol^–1 cm^–1 at 547 and 558 nm, respectively. The methods adhere to Beer's law for 0.13–1.83 µg cm^–3 of silver and 0.16–2.24 µg cm^–3 of gold and the corresponding sensitivities are 0.0015 and 0.0023 µg cm^–2. The methods were used successfully to determine trace amounts of silver and gold in silicate rocks and a sulfide ore.