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

Abstract 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 Cu 2+ over other transition metal ions. Mn 2+ , Co 2+ , Ni 2+ , Cd 2+ , and Zn 2+ ions were separated from Cu 2+ using HNO 3 eluent with the cyclenbowl column. The preconcentration of Cu 2+ in parts per billion level from a high concentration matrix of Mn 2+ , Co 2+ , Ni 2+ , Cd 2+ , and Zn 2+ ions was achieved in the cyclenbowl column using a nitric acid eluent gradient. Recovery of Cu 2+ at >98% was obtained based on direct interaction of metal ion and cyclen. Although Mn 2+ , Co 2+ , Ni 2+ , Cd 2+ , and Zn 2+ were not separated by HNO 3 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 HC 2 O 4 − ions that cooperate with cyclen sites in retaining transition metal ions.