Displacement chromatography mobile phases

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]. 

The profile of the concentration of a solute in both the mobile and stationary phases is Gaussian in form and this will be shown to be true when dealing later with basic chromatography column theory. Thus, the flow of mobile phase will slightly displace the concentration profile of the solute in the mobile phase relative to that in the stationary phase the displacement depicted in figure 1 is grossly exaggerated to demonstrate this effect. It is seen that, as a result of this displacement, the concentration of solute in the mobile phase at the front of the peak exceeds the equilibrium concentration with respect to that in the stationary phase. It follows that there is a net transfer of solute from the mobile phase in the front part of the peak to the... 

Suresh, V., Gallant, S., and Cramer, S., Immobilized metal affinity chromatography displacer characteristics of traditional mobile phase modifiers, Biotechnol. Prog., 12, 84, 1996. 

The first study that made it possible to estimate the critical length of a column in gradient HPLC of proteins was presented by Belenkii and co-workers in 1993 [53]. Their approach was based on the concept of critical chromatography of synthetic polymers. They introduced the concept of a critical distance, X0, after which the protein zone travels with the same velocity as the mobile phase (similarly to what has been shown previously by Yamamoto et al. [60]). The equation for the critical distance at which the zone velocity v(x) becomes virtually identical to the displacer velocity, u, is defined as ... 

Figure 3.2 Three major methods in chromatography. The commonest form of chromatography involves the introduction of a small volume of sample onto a column and is known as zonal chromatography. Movement down the column is effected by the mobile phase, which may be simply a solvent (A) allowing partition of the test molecules between the stationary and mobile phases. Alternatively, the mobile phase may be a solvent containing solute molecules (B), which actively displace test molecules from the stationary phase. A less frequently used method known as frontal separation (C) does not involve a separate mobile phase but a large volume of the sample is allowed to pass through the column and as the various components separate, concentration fronts develop and their movement can be monitored.

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... 

Liquid/Solid Chromatography (LSC) is adsorption chromatography. Adsorbents such as alumina and silica gel are packed in a column and the sample components are displaced by a mobile phase. Thin layer chromatography and most open column chromatography are considered liquid/solid chromatography. 

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