Size exclusion chromatography supports

VI. APPLICATION OF POLYMERIC BEADS AS SIZE EXCLUSION CHROMATOGRAPHY SUPPORTS... 

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. 

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. 

In 1971, Hiatt et al. found that polyethylene oxide (PEO) of molecular weight about 100000 prevented the adsorption of rabies virus to porous glass with an average pore diameter of 1250 A. The support was modified by passage of one void volume of 0.4% solution of the polymer in water, followed by 5 or more volumes of distilled water or buffered salt solution. The virus was effectively purified from the admixtures of brain tissue fluid by means of size-exclusion chromatography on the modified glass column [28]. 

In addition to the insoluble polymers described above, soluble polymers, such as non-cross-linked PS and PEG have proven useful for synthetic applications. However, since synthesis on soluble supports is more difficult to automate, these polymers are not used as extensively as insoluble beads. Soluble polymers offer most of the advantages of both homogeneous-phase chemistry (lack of diffusion phenomena and easy monitoring) and solid-phase techniques (use of excess reagents and ease of isolation and purification of products). Separation of the functionalized matrix is achieved by either precipitation (solvent or heat), membrane filtration, or size-exclusion chromatography [98,99]. 

The experimental techniques for the study of conformational branched properties in solution are the same as used for linear chains. These are, in particular, static and dynamic light scattering, small angle X-ray (SAXS) and small angle neutron (SANS) scattering methods, and common capillary viscometry. These methods are supported by osmotic pressure measurements and, nowadays extensively applied, size exclusion chromatography (SEC) in on-line combination with several detectors. These measurements result in a list of molecular parameters which are given in Table 1. 

It took a long time before the percolation theory could be proved to be the better one in most cases. The reason for this delay resulted in part from the fact that until ten years ago the size exclusion chromatography (SEC) with on-hne light scattering was not sufficiently well developed. A direct molar mass determination is, however, imperative, since the separation in SEC is due to the hydrodynamic volume of the particles. A branched macromolecule has, however, a significantly higher molar mass than a linear one of the same hydrodynamic volume. Since 1989 a number of results have been reported which all strongly supported the percolation theory [109,111-116]. 

Note 3 Macroporous polymers are used, for example, as precursors for ion-exchange polymers, as adsorbents, as supports for catalysts or reagents, and as stationary phases in size-exclusion chromatography columns. 

A related approach, termed dendrimer-supported combinatorial chemistry (DCC), has been disclosed by Kim et al. [23], It uses dendrimers as soluble supports (see Fig. 7). In this case the reactions are performed in solution and the dendrimeric intermediates are isolated/purified by size exclusion chromatography. The strategy was validated by the preparation of a 3 x 3 x 3 combinatorial library using the Fischer indole synthesis. 

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