Critical parameters of liquid chromatography at critical conditions in context of poloxamers: Pore diameter, mobile phase composition, temperature and gradients.

At the borderline between size exclusion chromatography (SEC) and interaction chromatography (IC) there is a special mobile phase composition and temperature at which polymer chains become "chromatographically invisible". This point is termed as "chromatographic critical point" and chromatographic separations performed using these conditions are called "liquid chromatography at critical conditions" (LCCC). LCCC is a powerful technique in the analysis of functional polymers and block copolymers. At these so-called critical conditions molar mass discrimination of any specific homopolymer is suppressed rendering elution of whole range of molar mass at same elution volume. These conditions allow enhanced separation with regard to non-critical segment either in exclusion or interaction regime of the polymer chromatography. This article is intended to critically discuss different parameters that can be maneuvered to improve separation and in turn characterization of non-critical segment of block copolymers at LCCC. Different experimental parameters evaluated in this study include pore size of the column, mobile phase composition, temperature and gradients. These parameters can be adeptly adjusted to improve separation of non-critical segment while keeping the other segment close to critical conditions. Current study demonstrates that pore diameter and mobile phase are the only practical variable that can be used for improvement of characterization of non-critical block in the block copolymer while non-critical block is in exclusion regime. On the other hand, pore diameter of the column, temperature, solvent composition and gradients are important parameters that can be skillfully tuned for improvement of separation of non-critical block while non-critical block elutes in interaction regime. The above-mentioned variations are evaluated for di-block as well as tri-block copolymers of A-B-A and B-A-B type. Moreover, LCCC-IC is especially important for analysis of poloxamers.