Liquid-liquid extraction and simultaneously spectrophotometric determination of Co (II) and W (VI) using crown ether (DB-18-C6) in aqueous media and in high speed steel
Résumé
An analytical reagent ether crown DB-18-C-6 was extensively used for the simultaneous and individual extraction and spectrophotometric determination of the tungsten and cobalt at microgram levels. The ligand reacts with two metals, and the ion-association systems were extractable into chloroform giving a yellowish [(DB-18-C-6 center dot NH4)(+)(2)[WO(SCN)(5)](2)] and [(DB-18-C-6 center dot NH4)(+)(2)[Co(SCN)4](2-)] complexes. The absorption peaks of these complexes were found overlapping at lambda max of 415 nm and 621.6 nm, respectively. Under optimum conditions, the [WO(SCN)(4)](2-)] complexation and extraction are possible only in concentrated medium (2.5 M of HCl). While, the [Co(SCN)4](2-)] was extractable at a pH range of 4-10. The linear ranges were 29.45-147.25 mu g mL(-)(1) for Co(II) and 1.8-183 mu g/mL for W(VI) with molar absorptivity, epsilon = 1.7 x 10(4) and epsilon = 1.6 x 10(4) dm(3) mol(-1) cm(-1), respectively. The accuracy and reproducibility of the proposed method for various amounts of cobalt and tungsten in their binary mixture were tested, and the effects of diverse ions on their extraction were also investigated. The developed method was successfully applied for the simultaneous determination of Co(II) and W(VI) in high-speed steel (HS2-9-1-8) containing 2% W, 9% Mo, 1% V, and 8% Co.