Selective extractive spectrophotometric determination of cobalt using cyanex 923

Abstract

The present paper describes a selective extractive spectrophotometric method for the determination of Co (II)using toluene solution of cyanex 923. A blue coloured complex (λ_max 685 nm) is quantitatively extracted in the organic phase from 7-10 mol L^-1 HCl. The composition of this complex is proposed as H₂CoCl₄.2cyanex 923 . The Beer 's law is obeyed in the concentration

range 0.0-4.2×10^-3 mol L^-1 Co(II) and the molar absorptivity of the complex is 5.6×10² L mol^-1 cm^-1. The presence of hundredfold excess of metal ions such as Mo(VI), W(VI), V(V), Ti(IV), V(IV), Al(III), Cr(III), Fe(III), Mn(III), Fe(III), Ni(II), Cu(II), Zn(II) and Cd(II) and fifty fold of anions namely PO₄^3-, SO₄^2-, C₂O₄^2-, citrate, tartrate, NO₃^- and SCN^- do not interfere in the determination of Co(II). The accuracy of proposed procedure is checked by assaying the concentration of cobalt in two standard NBS steel samples. The applicability of the method is demonstrated by selective determination of Co(II) in a multielement system like polymetallic manganese sea nodules. The result is in fairly good agreement with those obtained by AAS and ICPAES.