SEC packings

Due to the fact that the application area for Protein-Pak columns is more limited than the application area of other SEC packings, only a few pore sizes are needed for standard protein separations. A more detailed discussion of this product line follows in Section III,C. 

These problems can be associated with the fact that various pore size SEC packings, either in a bank of individual pore size columns or in a mixed gel column set, respond differently in this extremely polar solvent. In addition the... 

The major advantage of the capillary hydrodynamic chromatography is that the mobile phase does not need to have similar solubility parameter as the sample and packing material. (In SEC, nonsize exclusion effects may be observed if the solubility parameter of the sample, packing material, or mobile phase is considerably different.) Therefore, the hydrodynamic size of polymers can be studied in a 0 solvent and even in a solvent that is not compatible with any currently available SEC packing material (9). Figure 22.4 is an example of polystyrene separation in both THF and diethyl malonate. Diethyl malonate is the 0 solvent of polystyrene at 31-36 C. 

A multidimensional system using capillary SEC-GC-MS was used for the rapid identification of various polymer additives, including antioxidants, plasticizers, lubricants, flame retardants, waxes and UV stabilizers (12). This technique could be used for additives having broad functionalities and wide volatility ranges. The determination of the additives in polymers was carried out without performing any extensive manual sample pretreatment. In the first step, microcolumn SEC excludes the polymer matrix from the smaller-molecular-size additives. There is a minimal introduction of the polymer into the capillary GC column. Optimization of the pore sizes of the SEC packings was used to enhance the resolution between the polymer and its additives, and smaller pore sizes could be used to exclude more of the polymer... 

The porosity of an SEC column can be characterized by its phase ratio (VJV0). Soft-gel SEC packings have high porosities with phase ratios of 1.5 to... 

High-performance SEC packings have more modest phase ratios of 0.5 to... 

As in interactive modes of chromatography, reduction in particle diameter reduces mass transfer effects and improves column efficiency in SEC. Column packings with particle diameters of 10 to 12 pm are available for less demanding applications, whereas SEC packings with particle diameters of 4 to 5 pm can be used for applications requiring higher resolution. 

TABLE IV. PHYSICAL CHARACTERISTICS OP SEC PACKINGS FROM MERCURY POROSIMETRY... 

From these studies with SynChropak SEC packings and controlled porosity glass, it is concluded that the silica packing contains a population of micropores which are differentially accessible to low molecular weight probes of total permeation volume. It is not known, however, if the microporosity in the 100 and 300A SynChropak SEC packings is the result of the rather wide pore-size distribution and whether all silicas contain micropores. 

For the SEC analysis of polyelectrolytes, it is best to use a hydrophilic, polymeric packing or a surface-modified silica packing in which most of the silanols are derivatized. Another approach for the analysis of cationic polyelectrolytes is to use packings derivatized with cationic functional groups ( ). This is the basis of a commercially available SEC packing which is chemically bonded with polyethylenimine (W). 

Open tubular Gel Monolith Packed SEC Packed unmodified IPacked modified I ... 

These packings have an advantage over the more traditional silica SEC packings in that ... 

For organosoluble polymers cross linked polystyrene or silica based packings are used. For water soluble polymers various silica based and hydrophobic polymeric packings are used. Pore sizes of the SEC packings may range from 3 to 300 nm. 

Compared to SEC, a broader concept of universal calibration is possible with thermal FFF because thermal FFF channels do not contain the inherent variability associated with SEC packing materials. As a result, calibration curves are universal to all thermal FFF channels that use the same cold-wall temperature. A common cold-wall temperature is important because both D and Dj vary with temperature. 

Rather broad pore size distributions are generally found in this way for the polymeric SEC packings. This property widens the range of molecular sizes that can be determined by the polymeric column. In general, though, SEC columns based on macroporous sdica or sifica bonded phases function equally good. 

By far the most widely used organic SEC packings are based on porous polystyrene/divinylbenzene (PS/DVB) particles. This is primarily because of their... 

Mixed gel or linear SEC packings can be produced by blending together selected pore size gels and packing them as a homogeneous mixture to produce... 

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