Elution modified displacement chromatography

However, it is possible to modify almost any adsorbent so as to give linear isotherms (Chapter 4). so that this theoretical advantage of displacement over elution is of academic interest only. A quite specialized form of displacement chromatography, with fluorescent indicators added to the sample so as to mark band boundaries on the column 37), is still widely used in the petroleum industry for the routine analysis of gasolines. The extension of this technique to other sample types has been discussed 38) but has so far found no reported applications. 

For the given systems (ionizable selectors and solutes), a modified form of CPC was usually more favorable The so-called pH-zone-refining CPC mode, which is a kind of displacement type of chromatography. In this mode, the column is filled with the acidified stationary phase (e.g., using TFA as retainer), then injection of the sample takes place before the rotor is switched on and elution is started with a basic mobile phase (e.g., using ammonia as displacer in the aqueous mobile phase). Apparent pH and enantiomeric composition were determined for every fraction. It appeared that the enantiomers eluted in refined... 

The eluant systems used in adsorption chromatography are based on nonpolar solvents, commonly hexane, containing a small amount of a polar additive, such as 2-propanol. When the sample is applied, solute molecules with polar functionality will bond to the active sites on the packing they will subsequently be displaced by the polar modifier molecules of the eluant as the chromatogram is developed, and will pass down the column to be re-adsorbed on fresh sites. The ease of displacement of solute molecules will depend on their relative polarities. More polar molecules will be adsorbed more strongly, and hence will elute more slowly from the column. A system as described in Figure 4.1 may be used. It was the type of apparatus first used for chromatographic separations of the kind familiar today. 

Characterization of Displaced Protein. With labelled antithrombin III, chromatography of the displaced radioactivity on heparin-Sepharose revealed that the bulk of the displaced radioactive material did not bind to heparin-Sepharose (Table II). With arvinized plasma as the displacing eluent, 65% of the antithrombin III eluted in the void volume, compared with 49% of the control I-antithrombin III (diluted in citrated plasma) that had not previously been used to inactivate thrombin the latter unbound fraction was likely labelled impurities or inhibitor modified by radiolabelling to lose its heparin affinity. With 5% (w/v) albumin used as a displacing eluent, 78% of the I-antithrombin III came out in the void volume. This increase in material that did not bind to heparin after displacement from heparin-PVA was attributed to post-complex antithrombin III, a modification of the original inhibitor resulting from the inactivation of thrombin. Neither thrombin-antithrombin III complex nor free antithrombin III were detected in the 5% (w/v) albumin displaced fractions while there was a barely detectable amount of complex (6%) and free antithrombin III (4%) in the material displaced by arvinized plasma. With the control I-antithrombin III, 25% of the radioactivity was determined to be free antithrombin III and 2% as complex. The remainder (22-27%) was not recovered from the column. 

Indeed, one usually deals with retention of analytes on the stationary phase, which reduces the concentration of the analyte in the moving zone of the mobile phase and requires additional amounts of the mobile phase to elute the retained portion of the analyte from the stationary phase. Cases of peak compression in chromatography are mostly coupled with the displacement of the adsorbed portion of the analyte (or analytes) by an auxiliary component of the mobile phase (a displacer or mobile phase modifier). In order to act like this, the latter must be adsorbed on the stationary phase even stronger than the displaced analytes. Only in frontal analysis can several weaker retained components of a mixture be obtained with an enhanced concentration, at the expense of the stronger retained component that functions as a displacer and remains in the column [175]. 

---