Liquid adsorption chromatography under critical conditions

Entelis et al. (20) found that homopolymers of diflFerent molar masses show exactly similar retention behavior on silica if a special eluent mixture was used. They found that under criticaP conditions the sorbent did not see the polymeric nature of the chain. The separation was dependant only on the enthalpic interaction of the sample-sorbent pair [so-called critical chromatography or liquid adsorption chromatography under critical conditions (LACCC)] (20-24). 

The deformulation of a polyester was done with liquid-adsorption chromatography under critical conditions (LACCC) that was coupled to an SEC system. The dimension was separated by the end-group functionality to study byproducts formed during polycondensation. By 2D chromatography a number of species (e.g., cycles, ethers, alkyl terminated chains, and so on) could be identified. Some of them influenced the mechanical and thermal properties of the polyesters significantly. 

The principle of the liquid chromatography under critical conditions (LC CC) was elucidated in Section 16.3.3. The mutual compensation of the exclusion—entropy and the interaction—enthalpy-based retention of macromolecules can be attained when applying in the controlled way the interactions that lead to either adsorption or enthalpic partition. The resulting methods are called LC at the critical adsorption point (LC CAP) or LC at the critical partition point (LC CPP), respectively. The term LC at the point of exclusion-adsorption transition (LC PEAT) was also proposed for the procedures employing compensation of exclusion and adsorption [161]. It is anticipated that also other kinds of enthalpic interactions, for example the ion interactions between column packing and macromolecules can be utilized for the exclusion-interaction compensation. 

The chromatographic separation of polymers by liquid chromatography under critical conditions (LCCC), also referred to as liquid chromatography (LC) at the critical point of adsorption, LC in the critical range or LC at the point of exclusion-adsorption transition, has attracted significant attention within polymer community. Russian scientists using TLC [1-3] and later LC [4,5] have been the first experimentally identify critical conditions. At the critical conditions polymers of a given kind are eluted independently from their molar mass (for example. Fig. 1 [6]). 

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