Size exclusion chromatography materials

Two classes of micron-sized stationary phases have been encountered in this section silica particles and cross-linked polymer resin beads. Both materials are porous, with pore sizes ranging from approximately 50 to 4000 A for silica particles and from 50 to 1,000,000 A for divinylbenzene cross-linked polystyrene resins. In size-exclusion chromatography, also called molecular-exclusion or gel-permeation chromatography, separation is based on the solute s ability to enter into the pores of the column packing. Smaller solutes spend proportionally more time within the pores and, consequently, take longer to elute from the column. 

Conductivity detectors, commonly employed in ion chromatography, can be used to determine ionic materials at levels of parts per million (ppm) or parts per bUHon (ppb) in aqueous mobile phases. The infrared (ir) detector is one that may be used in either nonselective or selective detection. Its most common use has been as a detector in size-exclusion chromatography, although it is not limited to sec. The detector is limited to use in systems in which the mobile phase is transparent to the ir wavelength being monitored. It is possible to obtain complete spectra, much as in some gc-ir experiments, if the flow is not very high or can be stopped momentarily. 

Microspherical polymer beads are widely used as packing materials for chromatography and a variety of other applications. Size exclusion chromatography is based on pore size and pore-size distribution of microbeads to separate... 

Modern SEC columns are packed with material other than polystyrene gels, such as porous silica particles or highly cross-linked styrene-divinylbenzene copolymers. Because of improvements in speed and resolution, the term SEC is sometimes replaced by the term high-performance size-exclusion chromatography (HPSEC). 

Most size exclusion chromatography (SEC) practitioners select their columns primarily to cover the molar mass area of interest and to ensure compatibility with the mobile phase(s) applied. A further parameter to judge is the column efficiency expressed, e.g., by the theoretical plate count or related values, which are measured by appropriate low molar mass probes. It follows the apparent linearity of the calibration dependence and the attainable selectivity of separation the latter parameter is in turn connected with the width of the molar mass range covered by the column and depends on both the pore size distribution and the pore volume of the packing material. Other important column parameters are the column production repeatability, availability, and price. Unfortunately, the interactive properties of SEC columns are often overlooked. 

A. Packing Materials for Size Exclusion Chromatography (SEC) and HOPC... 

Chemically attached copolymers of iV-vinylpyrrolidone (N-VP) and N-(2-hydroxyethyl)acrylamide (N-HEAA) steeply decrease the inherent glass adsorp-tivity which is observed for proteins in aqueous buffer solutions. Thus, it became possible to apply the prepared materials to the size exclusion chromatography of viruses and ribosomes. 

The partially hydrolysed material was fractionated by size exclusion chromatography on a Bio Gel PIO (Bio Rad) column (2,6 x 90 cm) and eluted with 50 mM ammonium hydrogen carbonate at 20 ml/h and fractions of 3.2 ml each were collected. Fractions 45-70 were pooled and subjected to HPAEC-PAD for further separation. 

These new technological advances also have impacted the work of the American Society for Testing and Materials (ASTM). The ASTM committee D20.70.04 currently is involved in developing new size exclusion chromatography methods (GPC) that incorporate these advances. 

Size-exclusion chromatography (SEC) has been used to characterize the unimer-micelle distribution. However, SEC is not an absolute method and thus requires calibration. Since it is practically impossible to calibrate a SEC apparatus for the unimers and micelles formed by a block copolymer, only indicative MW values can be obtained. Moreover, several authors have noted a strong perturbation of the unimer-micelle equilibrium during SEC experiments even when interaction of the material with the SEC column was minimized [4,61,62],... 

The size-exclusion chromatography (or gel-chromatography) is a means of separation which is exclusively dependent on the exchange of solute molecules between the solvent of the mobile-phase and the same solvent within the pores of the column-packing material. In reality, it is the pore-size-range of the packing material that solely determines the molecular-size-range within which a particular separation can take place effectively. 

There are usually three types of materials that are employed in the size-exclusion chromatography for pharmaceutical substances which have been discussed briefly as under ... 

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