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

Abstract

An analytical reagent ether crown DB-18-C-6 was extensively used forthe simultaneous and individual extraction and spectrophotometricdetermination of the tungsten and cobalt at microgram levels. Theligand reacts with two metals, and the ion-association systems wereextractable into chloroform giving a yellowish [(DB-18-C-6∙NH4)+2[WO(SCN)5]2]and[(DB-18-C-6∙NH4)+2[Co(SCN)4]2-]complexes.Theabsorption peaks of these complexes were found overlapping atλmax of 415 nm and 621.6 nm, respectively. Under optimum condi-tions, the [WO(SCN)4]2-] complexation and extraction are possible onlyin concentrated medium (2.5 M of HCl). While, the [Co(SCN)4]2-]wasextractable at a pH range of 4–10. The linear ranges were 29.45–-147.25μgmL−1for Co(II) and 1.8–183 μg/mL for W(VI) with molarabsorptivity,ε=1.7×104andε=1.6×104dm3mol−1cm−1,respec-tively. The accuracy and reproducibility of the proposed method forvarious amounts of cobalt and tungstenintheirbinarymixtureweretested, and the effects of diverse ions on their extraction were alsoinvestigated. The developed method was successfully applied for thesimultaneous 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.