Size-exclusion chromatography column packings

The packed columns of Shodex OHpak SB-800HQ series are packed with polyhydroxymethacrylate gels and are designed for use with high-resolution, high-speed aqueous size exclusion chromatography. The packed columns are best suited for the analysis of water-soluble polymers and proteins (Table 6.8). 

Also, silica-based packings are available for aqueous size-exclusion chromatography. The commercially available ones are coated with a glycidoxypro-pylsilane bonded phase. While they do not swell or shrink, they are not compatible with basic pH values and contain residual silanols that may interact with the polymer. Also, only a limited pore-size range is available compared to the aqueous size-exclusion chromatography columns based on glycidyl methacrylate. 

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. 

A trend in chromatography has been to use monosized particles as supports for ion-exchange and size-exclusion chromatography and to minimize the column size, such as using a 15 X 4.6-mm column packed with 3-/rm polymer particles for size exclusion chromatography. The more efficient and lower back pressure of monosized particles is applied in the separation. 

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). 

High-performance size exclusion chromatography is used for the characterization of copolymers, as well as for biopolymers (3). The packings for analyses of water-soluble polymers mainly consist of 5- to 10-/Am particles derived from deactivated silica or hydrophilic polymeric supports. For the investigation of organosoluble polymers, cross-linked polystyrene beads are still the column packing of choice. 

Size exclusion chromatography (SEC, also known as GPC and GFC) has become a very well accepted separation method since its introduction in the late-1950s by works of Porath and Flodin (1) and Moore (2). Polymers Standards Service (PSS) packings for SEC/SEC columns share this long-standing tradition as universal and stable sorbents for all types of polymer applications. In general, PSS SEC columns are filled with spherical, macroporous cross-linked, pressure-stable, and pH-resistant polymeric gels. 

Styragel columns are compatible with most solvents commonly used in size exclusion chromatography. Exceptions are found on both sides of the polarity scale the use of standard general-purpose Styragel columns with aliphatic hydrocarbons or with alcohols (except hexafluoroisopropanol) and water is generally not recommended. However, it is possible to pack columns in special solvents for special-purpose applications. The interested user should contact Waters for additional information. 

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. 

The instrumentation of HdC, including a pump, an injector, a column (set), a detector, and a recorder or computer, is very similar to size exclusion chromatography SEC). The essence of this technique is the column. There are two types of HdC columns open microcapillary tubes and a nonporous gel-packed column. This chapter emphasizes column technology and selection and the applications of this technique on the molecular weight analysis of macromolecules. 

SEC, size exclusion chromatography OTHdC, open tubular hydrodynamic chromatography PCHdC, packed column hydrodynamic chromatography ThFFF, thermal field flow fractionation. 

A number of analytical techniques such as FTIR spectroscopy,65-66 13C NMR,67,68 solid-state 13 C NMR,69 GPC or size exclusion chromatography (SEC),67-72 HPLC,73 mass spectrometric analysis,74 differential scanning calorimetry (DSC),67 75 76 and dynamic mechanical analysis (DMA)77 78 have been utilized to characterize resole syntheses and crosslinking reactions. Packed-column supercritical fluid chromatography with a negative-ion atmospheric pressure chemical ionization mass spectrometric detector has also been used to separate and characterize resoles resins.79 This section provides some examples of how these techniques are used in practical applications. 

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