Cation separation and preconcentration using columns containing cyclen and cyclen-resorcinarene derivatives

The selectivity and separation of transition metal ions on two columns packed with cyclen-based macrocycles adsorbed onto 55% cross-linked styrene-divinylbenzene resin are presented. The N-cyclen and cyclen-resorcinarene stationary phases were made by adsorbing hydrophobically substituted N-cyclen or a cyclen-resorcinarene derivative (cyclenbowl) on the resin, respectively. The stability constants of cyclen with transition metal ions demonstrate that cyclen has selectivity for Cu²⁺ over other transition metal ions. Mn²⁺, Co²⁺, Ni²⁺, Cd²⁺, and Zn²⁺ ions were separated from Cu²⁺ using HNO₃ eluent with the cyclenbowl column. The preconcentration of Cu²⁺ in parts per billion level from a high concentration matrix of Mn²⁺, Co²⁺, Ni²⁺, Cd²⁺, and Zn²⁺ ions was achieved in the cyclenbowl column using a nitric acid eluent gradient. Recovery of Cu²⁺ at >98% was obtained based on direct interaction of metal ion and cyclen. Although Mn²⁺, Co²⁺, Ni²⁺, Cd²⁺, and Zn²⁺ were not separated by HNO₃ eluent, addition of oxalic acid yielded a very good separation. A retention mechanism is proposed for the latter system in which the protonated cyclen units attract negatively charged HC₂O₄⁻ ions that cooperate with cyclen sites in retaining transition metal ions.