Solid-phase enrichment (SPE) is a popular approach for the separation and enrichment of metal ions for the elemental analysis of environmental samples. In comparison with traditionally used methods for enrichment such as liquid-liquid extraction, SPE has several advantages - including higher throughput, simpler operation, lower cost, and higher recovery. Nevertheless, an important limitation of SPE columns with standard stationary phases has been their low selectivity. More recently, the use of ion-imprinting technology has enabled the highly selective adsorption of target analytes.

The key difference between these techniques lies in the nature of the interaction between metal ions with the ligand. In the case of ordinary SPE columns, various metal ions are able to bind with ligands - independently with regard to stereo-chemical interactions. In contrast, ion-imprinted polymers (IIPs) use function monomer to influence the combined action between template ion and imprinted sites in the polymers.

In the April issue of the Journal of Separation Science, Chinese researchers report the development of a novel IIP for the SPE enrichment of trace copper(II), and apply this approach to the elemental analysis of biological and natural water samples. Led by Xijung Chang of Lanzhou University, the group created a Cu(II)-IIP using (2Z)-N,N'-bis(2-aminoethylic)but-2-enediamide as the functional monomer and pentaerythritol triacylate (PETRA) as the crosslinker, thereby facilitating the highly selective extraction and quantification of trace copper ion.

In comparison with several recently published IIPs for Cu(II) enrichment, the polymer described here performs favorably. The selectivity coefficients - Cu(II) versus Co(II), Ni(II), and Zn(II) - are superior to most of these materials, being outperformed only by double-imprinted polymers (CS, AAPTS, and TEOS). As such, this novel Cu(II)-IIP should prove useful for the elemental analysis of aqueous samples.

Article by Zhai et al. on copper enrichment by SPE using ion-imprinted polymer, Journal of Separation Sciences, April 2008