Control of the retention selectivity of rare earth octaethylporphyrins in reversed-phase high-performance liquid chromatography using amines as mobile phase additives

Abstract

The reversed-phase liquid chromatographic retention behaviour of the complexes of octaethylporphyrin (OEP) with eleven trivalent rare earth (REs), viz., Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, on an octadecyl-bonded silica gel column is described. All these complexes can be eluted without demetallation with a methanol-water mixture that contains a small amount (about 1%) of acetylacetone and an amine. The retention order of the RE-OEP complexes depends on the amine used. With a mono- n-alkylamine and a di- n-alkylamine, the retention of the RE-OEP complex decreases with increasing atomic number of the REs within the lanthanide series, whereas the reverse tendency occurs with a trialkylamine and a dialkylamine possessing branched alkyl side-chains or alcoholic side-chains. In all instances, the retention of the Y complex is close to that of the Dy complex. Successful separation of the OEP complexes of Lu, Yb, Tm, Er and Sm in 20 min is demonstrated with dihexylamine.