Liquid Chromatography Of Synthetic Polymers Research Articles

Recent progress in liquid chromatography of synthetic polymers

Recent progress in liquid chromatography of synthetic polymers

Liquid chromatography of synthetic polymers under critical conditions of enthalpic interactions 4: Sample recovery

Reduced sample recovery is a frequent feature of LC of macromolecules under critical conditions of enthalpic interactions (LC CC). Several methods of assessment of LC CC sample recovery are compared. A novel approach is based on an online combination of the. The LC CC column with a noninteractive SEC column. It provides not only the amount but also the molar mass of the eluted/withheld polymer. The procedure was tested with poly(methyl methacrylate), bare silica gel column packings, and "critical eluent" tetrahydrofuran/toluene. It was shown that macromolecules with higher molar masses were preferentially trapped within the LC CC column packing so that the eluted part of the sample was no longer representative. The incomplete polymer elution can make the LC CC polymer analyses susceptible to significant experimental errors.

Two-dimensional liquid chromatography of synthetic polymers

Two-dimensional liquid chromatography, 2D-LC of synthetic polymers is critically assessed. Similarities and differences of 2D-LC of low-molecular-mass and polymeric substances are reviewed. The rationale of application of 2D-LC to macromolecular substances is discussed. Basic information on retention mechanisms in liquid chromatography of synthetic polymers is furnished. The principles, reasons, and significance of coupling of retention mechanisms are explained. The resulting separation processes are elucidated, and the technical concepts of the corresponding experimental arrangements are described. The benefits of 2D-LC are demonstrated together with numerous problems and shortcomings of the method.

Liquid Chromatography of Synthetic Polymers under Limiting Conditions of Insolubility III

AbstractSummary Performance was evaluated of silica based commercial monolithic rod‐like columns in liquid chromatography of synthetic polymers under limiting conditions of enthalpic interactions (LC LC). LC LC employs the barrier effect of the pore permeating and therefore slowly eluting small molecules toward the pore excluded, fast eluting macromolecules. Phase separation (precipitation) barrier action was applied in present study. The barrier was created either by the narrow pulse of an appropriate nonsolvent injected into the column just before the sample solution (LC LC of insolubility – LC LCI) or by the eluent itself. In the latter case, the polymer sample was dissolved and injected in a good solvent (LC LC of solubility – LC LCS). In LC LCI, polymer species cannot break thru the nonsolvent zone while in LC LCS they cannot enter eluent, which is their precipitant. Therefore, polymer species keep moving in the zone of their original solvent. Macromolecules eluting under the LC LC mechanism leave the column in the retention volume (VR) roughly corresponding to VR of the low molar mass substances and can be efficiently separated from the polymer species non‐hindered by the barrier action. The known advantages of monoliths were confirmed. From the point of view of LC LCI and LC LCS the most important quality of monolithic columns represents their excellent permeability, which allows both working at high flow rates and injecting very high (in the range of 5%) sample concentrations. Monolithic column tolerate also extremely high molar mass samples (M>10,000 kg · mol−1). On the other hand, the mesopores (separation pores) of the tested monoliths exhibited rather small volume and wide size distribution. These shortcomings partially impair the permeability advantage of monoliths because in order to obtain high LC LC separation selectivity a tandem of several monolithic columns must be applied. Presence of large mesopores also reduces applicability of monolithic columns for molar masses below about 50 kg · mol−1 because VRs of polymers eluted behind the barrier are similar to that of freely eluting species. The non‐ negligible break‐thru phenomenon was observed for the very high polymer molar masses largely eluting behind the barrier. It is assumed that the fraction of very large mesopores present in the monoliths or association/microphase separation of macromolecules may be responsible for this phenomenon. This is why the presently marketed SiO2 monolithic columns are mainly suitable for the fast purification of the LC LC eluting macromolecules from the polymeric admixtures non‐hindered by the barrier‐forming liquid. Still, monolithic columns have large potential in the LC LCI and LC LCS procedures provided size (effective diameter) of the mesopores can be reduced and their volume increased.

Liquid chromatography of synthetic polymers under limiting conditions of insolubility. I. Principle of the method

AbstractA novel liquid chromatographic procedure is presented. It is based on differences in the transport velocities of the fast-moving, pore-excluded macromolecules and slow-progressing, pore-permeating small molecules of an auxiliary liquid. A barrier of small molecules selectively decelerates certain kind of macromolecules while other kind remains unhindered. As a result, polymers of different nature are efficiently separated. In this new approach, the barrier is formed by a zone of a non-solvent injected immediately before the sample solution. The resulting method is denoted liquid chromatography under limiting conditions of insolubility.

Limited sample recovery in coupled methods of high-performance liquid chromatography of synthetic polymers

AbstractComplex polymer systems, which exhibit multiple distributions in their molecular parameters can be characterized by coupled liquid chromatographic methods. The latter combine entropic (exclusion) and enthalpic (interaction) retention mechanisms. However, recent experimental results suggest that some coupled liquid chromatographic methods may suffer from incomplete sample recovery. This refers, for example, to liquid chromatography under critical conditions of enthalpic interactions and to eluent gradient liquid chromatography. Sample recovery in both latter methods was investigated for selected model systems applying adsorption retention mechanism. Reduced sample recovery was confirmed for both methods. It was revealed that even very high final strength of mobile phase may be insufficient for complete elution of polymer samples in eluent gradient polymer liquid chromatography.

Critical Conditions and Limiting Conditions in Liquid Chromatography of Synthetic Polymers

AbstractDistinctions between liquid chromatography of synthetic polymers under critical conditions (LC CC) and liquid chromatography under limiting conditions (LC LC) are elucidated. Surface adsorption retention mechanism of macromolecules is employed in the chromatographic systems composed of 10 and 30 nm pore diameter bare silica gels, poly (methyl methacrylate)s of different molar masses, and mixed eluents acetonitrile/dichloromethane of different compositions, and at different temperatures. Increased robustness of the LC LC methods compared to LC CC is confirmed: the LC LC elution behavior is much less sensitive to eluent composition changes compared to LC CC. Still, the LC CC system under study is, surprisingly robust in terms of temperature variations. LC LC methods produce narrow, focused polymer peaks while a peak broadening is observed in LC CC. The results demonstrate importance of sample solvent applied in the isocratic coupled polymer HPLC methods.

Liquid Chromatography of Synthetic Polymers under Critical Conditions. The Case of Single Eluents and the Role of ϑ Conditions

As a rule, critical conditions in liquid chromatography of synthetic macromolecules are adjusted by both mixed mobile phase composition and temperature. The application of single component eluents is attempted in the present study. The enthalpic interactions in the column are controlled exclusively by temperature. Poly(methyl methacrylate)s (PMMA), poly(n-butyl methacrylate)s (PnBMA), and polystyrenes (PS) in various solvents are investigated with bare silica gel and silica C18 bonded phases. Using a series of single eluents based on various esters, PMMA probes, and bare silica gel, it is shown that minute variations in eluent nature strongly affect polymer retention, and temperature represents a too weak parameter to adjust critical conditions in thermodynamically good solvents. The idea is proposed and tested that the sensitivity of polymer retention toward temperature variations increases in the vicinity of ϑ conditions, where the structure of macromolecules in solution strongly depends on temperature. The critical conditions have been identified in some single eluents which are thermodynamicaly poor solvents for polymers investigated, namely, acetonitrile for PMMA at 66 °C and dimethylformamide for PnBMA at 154 °C and for PS at 95 °Call with C18 bonded silica gel. A “critical-like” elution was also observed in cyclohexane for PS at 9 °C with silica gel C18 packing, which is well below the ϑ temperature. It is demonstrated that poly(methyl methacrylate)s can be separated according to stereoregularity in the area of critical conditions using acetonitrile eluent and silica C18 column packing. The excessive polymer peak broadening and decreased recovery which were observed in some mixed mobile phases are diminished in the single component critical eluents studied, but they are not fully eliminated.

Liquid chromatography of synthetic polymers: Principles and applications (in French)

Liquid chromatography of synthetic polymers: Principles and applications (in French)

Sample size and retention values in gradient liquid chromatography of synthetic polymers

Retention times in gradient liquid chromatography of synthetic polymers are often dependent on sample size. They increase with column load if the separation mechanism is governed by a solution process but decrease with increasing load if the mechanism is governed by adsorption. Since retention times independent of sample size are a prerequisite for peak identification as well as for the correct measurement of elution bands of samples with a broad distribution, measures to counteract sample-size effects deserve attention. Usually both solubility and adsorption are effective in gradient liquid chromatography of synthetic polymers. An appropriate balance of both effects is suitable for diminishing the influence of sample size on retention time of synthetic polymers. Ternary gradients allowing independent control of solubility and adsorption are promising.

Hydrolysed macroporous glycidyl methacrylate-ethylene dimethacrylate copolymer sorbent for size-exclusion high-performance liquid chromatography of synthetic polymers and biopolymers

Les groupes epoxy sont hydrolyses pour ameliorer leur hydrophilicite. Separation de proteines, de polystyrene