Spectrophotometric Determination of Cobalt(II) with Eriochrome Black T after Extraction as Methyltrioctylammonium Tetrathiocyanatocobaltate(II)

Abstract

Abstract A sensitive extraction-spectrophotometrie method for determination of cobalt(II) with Eriochrome Black T is described, which involves the preliminary separation of cobalt from aqueous solution by the benzene extraction of methyltrioctylammonium tetrathiocyanatocobaltate(II). The quantitative formation of ion pair between cobalt–Eriochrome Black T complex anion and the quaternary ammonium cation is attained by shaking the resulting extract with aqueous Eriochrome Black T solution of pH 5.5–8.2. Beer’s law holds for 0.57–4.0 μg cobalt in 5 ml of the extract with the molar absorption coefficient of ε587=6.62×104 cm−1 mol−1l (Sandell sensitivity 8.90×10−4 μg cm−2). The composition of the extracted ion pair is estimated to be cobalt: Eriochrome Black T:methlytrioctylammonium ion=1:2:3.