Liquid chromatography under critical conditions

Liquid Chromatography under Critical Conditions of Enthalpic Interactions.478... 

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 applicability of LC LC to the (ultra) high-molar-mass polymers. Contrary to liquid chromatography under critical conditions, LC LC likely exhibits no upper limit of the sample molar mass [234]. On the other hand, if the difference in elution rates of the barrier forming small molecules and the oligomeric species is too small, the LC LC separation becomes insufficient. As a result, LC CC and LC LC may be considered mutually complementary from the point of view of their applicability in the... 

D. Berek, Mater. Res. Innovat. 4, 365, 2001 Round Table Discussion Characterization of block copolymer with liquid chromatography under critical conditions of enthalpic interactions, in International Conference on Coupled, Hyphenated and Multidimensional Liquid Chromatographic Procedures for Separation of Macromolecules, Bratislava, Slovakia, 2001. 

LCCC Liquid chromatography under critical conditions... 

A few years later, by using the same experimental procedures, the same scientists prepared cyclic polybutadienes170 (Scheme 82). THF was the polymerization solvent, which results in a 60% 1,2-content. From the g values was concluded that some of the cyclic polybutadienes (PBd) were contamined by their linear precursors. A high-resolution column set was used in order to separate the linear from the cyclic polymer. In this work the characterization analysis was the most comprehensive presented so far. Recently, these cyclic PSs were analyzed by high-pressure liquid chromatography under critical conditions, which is a method that can separate linear and cyclic macromolecules according to their archi-... 

Figure 12.5 Comparison of size exclusion chromatography (SEC) and liquid chromatography under critical conditions (LCCC) for the bulk enzymatic polymerization of caprolactone in the presence of bifunctional initiator 3 as a function of time. LCCC shows...

LIQUID CHROMATOGRAPHY UNDER CRITICAL CONDITIONS OF ENTHALPIC INTERACTIONS... 

The important issue of 2D-LC represents the abovementioned transfer of column effluent between the Id and the 2d columns, which can be done either off-line or online. In the off-hne approach, the fractions from the Id column are collected and successively re-injected into the 2d column. In this case, the unit TF is just a fraction collector. The macromolecules within particular fractions from the Id column are immixed so that resulting overall separation selectivity may be challenged. Moreover, entire procedure is laborious and slow. Various approaches were elaborated for the online transfer of fractions from the Id column into the 2d column. Often, the fractions from the Id column are cut into small parts that are one-by-one gradually transported into the 2d SEC column for independent characterization. This is the method of choice if the first-dimension separation produces broader peaks, such as it does liquid chromatography under critical conditions of enthalpic interactions, LC CC (see section 11.8.3). The operation principle of such chop-and-reinject method is evident from Figure 22. In this case, the TF unit from Figure 21 is a switching valve. 

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]). 

After reductive degradation, the gels were analyzed by liquid chromatography under critical conditions (LCCC) for polyMMA. The chromatograph was equipped with a Waters 600 controller and pump. The mobile phase was a mixture of butanone and cyclohexane (74 26 by volume). 

A combination of liquid chromatography under critical conditions using coupled density and RI detection in one dimension, and gradient high performance liquid chromatography in the second dimension, was used in the two-dimensional chromatographic analysis of the oligomers present in fatty alcohol ethoxylates. Full resolution was achieved. 6 refs. 

---