Improvements in Polymer Characterization by Size-Exclusion Chromatography and Liquid Chromatography at the Critical Condition by Using Enhanced-Fluidity Liquid Mobile Phases with Packed Capillary Columns

Abstract

Microscale chromatography has found numerous applications in liquid chromatography. The combination of enhanced-fluidity liquid mobile phases with packed-capillary LC is evaluated for polymer characterization using size-exclusion chromatography (SEC) and liquid chromatography at the critical condition (LCCC) phase. Separations of polystyrene polymers and copolymers are completed using liquid chromatography at the critical condition. The critical conditions of polystyrene polymers were approached by changing the concentration of CO(2) in the mixture combined with temperature and pressure variation. Because the solvent strength of enhanced-fluidity liquid mixtures is affected by temperature and pressure variation, the solvent strength could be fine-tuned to accurately find the critical condition. Long packed capillaries could be used in this application because the enhanced-fluidity mobile phases have low viscosities. High efficiencies resulted. The performance of packed-capillary and analytical-scale analytical columns containing the same packing material was compared for a challenging separation at the critical condition.

Characterization of Polystyrene-b-polyisoprene Diblock Copolymers by Liquid Chromatography at the Chromatographic Critical Condition

“…At this condition the retention of the homopolymer would become independent of molecular weight. The study on this interesting feature was started in the 1970s, , which has been supported by a number of experimental studies ,− although there remains some controversy as to whether such a precise coelution condition indeed exists. , Furthermore, other anomalies such as limited recovery for high molecular weight polymers as well as peak broadening and/or splitting have been reported at the critical condition. , Nevertheless, the critical condition has been successfully employed for the chromatographic separation of the components in polymer blends , and for the separation of polymers with respect to the terminal functional group. ,,− This technique is variously termed: liquid chromatography at the critical condition (LCCC), liquid chromatography at the point of exclusion−adsorption transition (LC-PEAT), or liquid chromatography at the critical adsorption point (LC-CAP). Another interesting application of the technique is the characterization of block copolymers. ,− The application is based on the assumption that a block at the critical condition is chromatographically “invisible”, and the retention of the block copolymer is supposed to be governed solely by the other blocks in the block copolymer.…”

Chapter 5 Size-exclusion chromatography

“…Capillary SEC affords an alternative separation strategy for microscale purification [63][64][65][66][67][68][69][70][71]. Capillary SEC columns are best suited for direct coupling to electrosprayionization mass spectrometry (ESI-MS), because they have comparable flow-rates that can be delivered to the ESI source without splitting.…”

Physicochemical properties of enhanced-fluidity liquid solvents

“…EFLC was found to be markedly more efficient and often have higher selectivity than when using supercritical fluid chromatography or conventional HPLC. The low viscosity of EF liquids has also allowed the use of long (1 m or more) capillary columns to produce highly efficient separations [3].…”