Coupling Size Exclusion Chromatography Research Articles

Separation of polymer and on-line determination of several antioxidants and UV stabilizers by coupling size-exclusion and normal-phase high-performance liquid chromatography columns

A procedure consisting of connecting in series two different HPLC columns, one for size-exclusion chromatography (SEC) and the second one a normal-phase (silica) column has been developed. An automatic three-way switching valve was placed between the two columns. Through the valve, the polymer was drained whereas the rest of the compounds, a group of antioxidants and UV stabilizers, were separated and analyzed in the second column. The behaviour of the SEC column in different organic phases is studied. Detection limits about 0.1 μg ml −1 were obtained for BHT, Tinuvin 326 and Tinuvin 327; 0.2 μg ml −1 for Irganox 1076, and 1.1 μg ml −1 for Cyasorb UV 9 and Cyasorb UV 1084. R.S.D. values of the whole process are lower than 4%.

Characterization of chitosans via coupled size-exclusion chromatography and multiple-angle laser light-scattering technique

Chitosan [(1 → 4)-2-amino-2-deoxy-β- d-glucan], a cationic biopolymer, was obtained by deacetylation of chitin samples from various sources. Nine chitosan samples differing in their degree of acetylation and molecular weight were used in this study. They were characterized by size-exclusion chromatography (SEC) coupled to a multiple-angle laser light-scattering (MALLS) photometer. The results show that accurate, reliable, and reproducible molecular weight and radius of gyration data are obtained by using SEC-MALLS. These samples were also characterized by a conventional secondary calibration technique. The molecular weights obtained by secondary calibration were found to be 2–3 times higher than those obtained using SEC-MALLS. The dissimilarity between the chitosan samples and polymer standards employed for calibration were presumed to be responsible for overestimation of the molecular weights. Therefore, we conclude that the unavailability of chitosan polymer standards underscores the need of an absolute molecular-weight determination technique, such as SEC-MALLS. This technique can be used for establishing structure-function relationships of chitosans and as a quality control tool for monitoring bulk production of chitosans.

Insight into the structure of pectin by high performance chromatographic methods

Various high performance chromatographic methods (analytical and preparative size exclusion chomatography, as well as ion exchange chromatography) have been developed in order to provide a deeper insight into the structure of pectin. The study mainly concentrated on commercial high-methoxy samples and products from the MRS research centre. By coupling size exclusion chromatography (SEC) and low angle laser light scattering (LALLS), realistic values of the molecular weight and molecular weight distribution can be obtained, as the contribution from aggregates may be easily determined. Differences between apple and lime pectin are shown. Preparative size exclusion chromatography allowed us to obtain information about the dependence of pectin composition on molecular weight by analysing the neutral sugars, the degree of esterification and the acetyl content in each individual molecular weight fraction. It was found that the high content of abrabinose and galactose in the low molecular weight fractions was associated with the ballast of free polysaccharides that accompany the actual pectic chain in all natural pectins. High resolution ion exchange chromatography was used to compare the intermolecular distribution of degrees of esterification (DE). Distributions of DE were found to be very narrow, with very few exceptions and by analysing SEC fractions, they were found to be constant with the molecular weight in all cases.

Stereoassociation of poly(methyl methacrylate): A study by coupling size exclusion chromatography with light scattering

We have studied the stereoassociation of two pairs of iso- and syndiotactic PMMAs of different tacticity by gel permeation chromatography. We have added a detector of scattered light at 90° to the chromatographic system in order to detect variations of light scattering. This experimental system has allowed us to follow the formation of stereocomplex particles, observing the changes in concentration and scattered intensity chromatograms obtained by injecting stereocomplex samples throughout stereocomplexation. We have studied also the influence of the stereoregularity of the syndiotactic PMMA used, finding great differences in the scattered light by the stereocomplex particles.

Molecular weights of solubilized lignite macromolecules

The determination of molecular weights and molecular weight distributions in humic acids derived from lignite by base extraction has been successfully carried out by low-angle laser light scattering (LALLS) photometry and by coupling size exclusion chromatography (SEC) with LALLS photometry. Since light scattering techniques give absolute molecular weight values, no error-prone calibrations of the size exclusion column were necessary. Reduction of soluble derivatives of the humic acids with zinc in acetic anhydride was required to reduce the optical absorbance so that a linear scattering response was observable. Weight average molecular weights of ≈ 1.3 × 10 6 and low polydispersity ratios were obtained for humic acid derivatives of Beulah, ND, lignite. Extension of this technique to the study of the more highly crosslinked humin which comprises the major portion of the lignite was investigated by treatment of the lignite with sodium hydroxide solution in a blender. This treatment converted up to 90% of the lignite into humic acids, which could be derivatized and studied by the LALLS techniques. The molecular weights of the products from lowtemperature solubilization of the lignite are inversely proportional to the per cent conversion.

Etude du couplage chromatographie d'exclusion‐diffusion de la lumière, 1. Dispositif expérimental et étude de polystyrènes «références»

AbstractThe possibilities of coupling size exclusion chromatography with light scattering (GPC‐DDL) are studied. The continuous light scattering detector is a modified (laser He‐Ne excitation) classical light scattering apparatus Fica 42000, equipped with a flow cell of low capacity (120μl). With this cell, a detection of the scattered light is obtained only at an angle of 90°. The light scattering detector is coupled with a GPC apparatus (packed with 10 μm gel particles). The precision, reproducibility and limitation to obtain molecular weight distribution curves of “standard” linear polystyrenes are studied.