Size elution chromatography

The principle of size elution chromatography is illustrated schematically... 

The principle of size elution chromatography can be used to prepare polyethylene fractions on a large scale. This requires exUemely large columns, which may be several orders of magnitude larger than those used for analytical scale size elution chromatography. 

An unusual application of size elution chromatography is the determination of lamellar thicknesses in high pressure crystallized polyethylene [4]. Nitric acid etching was used to remove all but the crystalline molecular stems, which were... 

Viscometry encompasses a number of methods by which viscosity is determined from the flow properties of a solution in a capillary tube. Either the rate of flow or resistance to flow can be measured. The former is most commonly used as a stand-alone technique, while the latter is principally used for on-line detection in size elution chromatography. Both require that the polymer solution be at an accurately known temperature in the region of 135°C. 

Fractionation of polyethylene has been accomplished by a wide variety of techniques other than size elution chromatography and temperature rising elution fractionation, with a multitude of variations thereon. The most notable of these less widely employed techniques include crystallization analysis fractionation [13], solvent gradient elution [14], successive solution fractionation (SSF) [15], continuous countercurrent extraction [16], high temperature thermal field-fiow fractionation [17], supercritical fluid fractionation (SCF) [18,19], and high pressure Soxhlet extraction [20]. 

In an alternative method the eluent Irom a temperature rising elution fractionator is collected as a series of fractions. These fractions are eoneentrated and subjected to size elution chromatography to determine their moleeular weight... 

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. 

In size-exclusion chromatography, the smallest solute that can be separated from other solutes all smaller solutes elute together. 

It is basically a fractionation process that depends not only on molecular size, but also on chemical composition, stereo-configuration, branching, and crosslinking. For multicomponent systems, fractionation with different ion polymolecularity, chemical heterogeneity and sequence length distribution, solubility or elution fractionation is of primary importance. Therefore, gel permeation chromatography or size exclusion chromatography is used as an important tool for the characterization of PBAs. 

Size exclusion chromatography has been used to analyse the size distribution of liposomes. For example, SUV can be separated from MLV, which elute in the void volume, by using a Sepharose 4B gel. 

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. 

A new direct method for using size exclusion chromatography (SEC) to evaluate polymer intrinsic viscosity [n] is discussed. Sample viscosity information is obtained by combining SEC elution curve data and calibration data using direct SEC-[n] calibration procedures without involving polymer molecular weight calculations. The practical utility, convenience and the expected precision of the proposed method are illustrated. 

Size exclusion chromatography (SEC) separates molecules of a polymer sample on the basis of hydrodynamic volume. When the chromatograph is equipped only with a concentration-sensitive detector, i.e. conventional SEC, a molecular weight distribution (MWD) can be obtained from the chromatogram only through use of a calibration function relating molecular weight and elution volume V (2). 

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