Abstract
Summary: Liquid chromatography under limiting conditions of insolubility (LC LCI) is a novel member of the group of liquid chromatographic methods working under limiting conditions of enthalpic interactions (LC LC). These employ differences in the velocity of small, pore permeating molecules (eluent components, auxilliary substances) and large, excluded macromolecules (sample components) in the course of their transport along an LC column packed with porous particles. A “barrier” of slowly moving small molecules of an appropriate nature selectively decelerates certain kinds of macromolecules due to their enthalpic interactions either with the column packing mediated by the barrier or with the barrier itself. The retained macromolecules accumulate on the barrier edge and elute from the column independently of their molar mass. Other kind(s) of macromolecules may be inert towards the barrier effect and elute in the exclusion mode. In this way, polymer species of different natures can be easily and efficiently separated. In LC LCI, a barrier impermeable to macromolecules consists of a narrow zone of non‐solvent, which is injected into the column immediately before the sample solution. The effects of basic experimental variables on the LC LCI elution of selected model polymer species were studied in the present work. These included both the polarity and pore size of the column packing, the nature and composition of the eluent, sample concentration and volume and the non‐solvent barrier width, as well as temperature. The general LC LCI behavior of macromolecules was confirmed. It was only slightly affected by the experimental conditions mentioned above, as long as the precipitation power of the non‐solvent barrier remained high enough. It has been demonstrated that LC LCI operates over a very broad polymer molar mass range, from a few thousand g · mol^−1^ up to several million g · mol^−1^. Under well chosen experimental conditions, LC LCI produces well focused polymer peaks, even for extremely large sample volumes reaching 16% of the total column volume. Narrow pore column packings are preferred because wide pore materials may produce skewed or even split LC LCI peaks. Chromatographically strong eluents and barrier components prevent adsorption of the sample on the column packing so that the mixed retention mechanism is avoided and the elution behavior of macromolecules is controlled exclusively by their solubility. In conclusion, LC LCI is a robust, user‐friendly technique which can help solve numerous separation problems in polymer science. For example, LC LCI enables fast and efficient separation of polymer species, which differ in their chemical composition.
Fast and efficient separation of the LC LCI eluted polystyrene from the SEC eluted poly(methyl methacrylate) of similar molar mass.
magnified imageFast and efficient separation of the LC LCI eluted polystyrene from the SEC eluted poly(methyl methacrylate) of similar molar mass.