AbstractThe complex formation of divalent ions, Mn, Co, Ni, Cu, Zn, Cd; the trivalent ions, Fe, Y, La‐Lu and U ion with eiknogen have been investigated spectrophotometrically and potentiometrically in 75% (v/v) dioxane. The metals form 1:1 and 1:2 complexes. Stability constants log K1and log K2are determined. The complexes formed have been characterised by elemental analyses and infra‐red spectral data from which bonding mode have been suggested.Phenolic ligands are frequently used as complexing agents for the detection and determination of metal ions in solution1,2. Eiknogen (1‐amino‐2‐naphthol‐4‐sulphonic acid) is usually used for the determination of low silicate and arsenate ion concentrations3, however, few studies on metal chelates with eiknogen are also reported. It was considered, of interest, to study the complex formation of some transition metals with eiknogen and determination of their structures and stabil