Chromatography metal-chelate adsorption

In metal chelate adsorption chromatography a metal is immobilised by partial chelation on a column which contains bi- or tri- dentate ligands. Its application is in the separation of substances which can complex with the bound metals and depends on the stability constants of the various ligands (Porath, Carlsson, Olsson and Belfrage Nature 258 598 I975 Loennerdal, Carlsson and Porath FEES Lett 75 89 1977). 

Liquid chromatography is rather more widely applicable than gas-liquid chromatography and in some forms has the capability to handle larger amounts of substance. All the main forms of LC are used, namely adsorption, partition, ion exchange, and gel filtration, and some newer forms of chromatography including metal-chelate adsorption, hydrophobic adsorption, and, particularly for biochemicals, affinity chromatography. 

Hetaeric chromatography, 230, 231 effect of charge on hetaeron, 233 retention model of, 231-238 Hetaeron. 191, 230, 231, 240, 243, 249, 280 see also Complexing agent adsorption on the stationary phase, 231, 249,230 amphiphilic, 243 cetrimide, 248 decylsulfonate, 230 dodecylbenzenesulfonate, 230 formation constant of complexes, 276 lauryl sulfate, 230 metal chelating, 262 micelle formation, 230 optically active, 262 surface concentration of, 232... 

Figure 8.2 Variants of affinity chromatography, (a) biospecific AC (b) metal chelate chrom. (c) charge transfer adsorption chrom. (d) hydrophobic interaction chrom. and (e) covalent chrom. (chemisorption). Abbreviations E = enzyme, L = amino acid group, me = meted ion, Rw = electron - withdrawing substituent, Rr = electron -donating substituent taken from ref. (47) with permission.

Immobilized metal ion affinity chromatography (IMAC) rehes on the ability of certain amino acid side chains to form coordinate bonds with immobilized metal ion complexes [6,181-186]. The adsorption of proteins mainly takes place through interactions with the imidazole ring of histidines. For other amino acids with electron donor atoms in their side chains, binding tends to be weak. Cysteines in natural proteins, are rarely available in an appropriate reduced form for binding to chelated metal ions. 

Other separation techniques have been proposed, such as membrane separation, adsorption, chromatography, pervaporation [91], and the use of chelating agents (but essentially for extraction of metal ions). 

---