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.