Stationary phases metal chelates

Thin-Layer Chromatography Stationary phase Metal Chelates Poly(saccharide) Derivatives... 

Although varying the concentration of salt in the eluent usually modulates the retention of proteins in MIC, the nature of the salt also plays an important role. It was found that stationary phases with chelates of soft and intermediate metals bind protein more strongly in the presence than in the absence of antichaotropic salts [21 ]. In a study using EDDA-silica supports, the elution strength of sodium salts on an Fe " " column was chloride < acetate < formate < phosphate for several proteins, whereas the strength on a Co column was acetate < phosphate <... 

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... 

Even more generally applicable are GC columns with chiral metal chelates as stationary phases (complexation gas chromatography)26 (Table 6). Quite recently, chiral GC methods have been developed on the basis of cyclodextrin derived stationary phases27. 

A limiting factor of complexation gas chromatography is the low temperature range (25-120°C). Therefore, improved thermostable polymeric stationary phases, e.g., Chirasil-Metal, in which the chiral metal chelates are chemically anchored to a polysiloxane backbone, have been prepared155 156. 

Metal chelate and bioaffinity chromatography based on the affinity of the protein for a specific molecule that can be incorporated in the stationary phase (not commonly used for food analysis)... 

The metal chelates are usually prepared from acetylacetone or trifluoroacetylacetone and are dissolved in a small quantity of stationary phase for the injection and separation. The UV absorbance of the derivatives is measured at 310 nm in a monitor equipped with a microflow cell. The separation of six metal acetylacetonates is shown in Fig.4.33 (column, SO cm X 2.7 mm I.D. particle diameter, 5-10 /am flow-rate, 1.8 mm/sec). 

In this reversed phase high performance liquid chromatographic method for neutral and cationic metal chelates with azo dyes, tetraalkylammonium salts are added to an aqueous organic mobile phase. The tetraalkylammonium in salts are dynamically coated on the reversed stationary support. As a result of the addition of tetraalkylammonium salts, the retention of the chelates is remarkably reduced. Tetrabutylammonium bromide permits rapid separation and sensitive spectrophotometric detection of the vanadium(V) chelate with 2-(8-quinolylazo)-5-(dimethylamino)-phenol, making it possible to determine trace vanadium(V). 

Affinity Chromatography was initially defined as a method based on specific and reversible molecular interactions between biologically active substances. However, the method has extended to non-biological stationary phases, such as metal-chelate complexes. This technique is used for separation and purification of proteins and other biologic materials, such as viruses and cells.47,48 A survey of various stationary phases and affinity interactions is given in figure 8.2. 

The peak shapes of metal chelating analytes are often poor because metal impurities in the stationary phase behave as active sites characterized by slowo desorption kinetics and higher interaction energies compared to reversed phase ligand sites. This phaiomaion is typical of silica-based stationary phases [31] ultrapure silicas were made commercially available to reduce it. However, styrene-divinylbenzene-based chromatogripliic packings suffer from the same problem and it was hypothesized that metals may be present in the matrix at trace conditions because they were used as additives in the polymerization process they may have been c tured via Lewis acid-base interactions between the aromatic ring n electrons and impurities in the mobile phase [32]. 

Cecchi, T. et al. Influence of metal impurities sorption onto a sihca based C18 stationary phase on the HPLC of metal chelating analytes. J. Liq. Chromatogr. Rel. Technol. 1999, 22, 429-440. 

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