H.E.J. Research Institute of Chemistry, International Centre for Chemical and Biological Sciences (ICCBS), University of Karachi, Karachi, 75270, Pakistan.
J Chromatogr A. 2020 Jan 4;1609:460440. doi: 10.1016/j.chroma.2019.460440. Epub 2019 Aug 8.
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.
在尺寸排阻色谱（SEC）和相互作用色谱（IC）的边界处，存在一种特殊的流动相组成和温度，在该温度下聚合物链变得“色谱不可见”。这一点被称为“色谱临界点”，使用这些条件进行的色谱分离称为“临界条件下的液相色谱（LCCC）”。LCCC 是分析功能聚合物和嵌段共聚物的有力技术。在这些所谓的临界条件下，任何特定均聚物的摩尔质量歧视都被抑制，从而在相同的洗脱体积下洗脱整个摩尔质量范围。这些条件允许在聚合物色谱的排除或相互作用区域中对非关键段进行增强分离。本文旨在批判性地讨论可以操纵的不同参数，以改善 LCCC 中嵌段共聚物非关键段的分离和表征。本研究评估了不同的实验参数，包括柱的孔径、流动相组成、温度和梯度。这些参数可以巧妙地调整，以改善非关键段的分离，同时使其他段接近临界条件。目前的研究表明，孔径和流动相是唯一可用于改善嵌段共聚物中非关键嵌段特征的实际变量，而非关键嵌段处于排除区。另一方面，柱的孔径、温度、溶剂组成和梯度是重要的参数，可以巧妙地调整，以改善非关键嵌段在相互作用区洗脱时的分离。上述变化适用于 A-B-A 和 B-A-B 型的二嵌段和三嵌段共聚物。此外，LCCC-IC 对分析泊洛沙姆尤其重要。
