Polymeric packings, size exclusion

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. 

According to the theory of SEC, aU partially excluded analytes elute in a relatively narrow window between the interstitial volume and the hold-up volume of the column. The interstitial volume of a column packed with a beaded material of broad bead size distribution amounts to about 40% of the column volume [144]. In addition to this volume, the mobile phase (water) also occupies the porous volume within the sorbent. In the case of our polymeric packings, the total pore volume amounted to about half of the polymer volume. AU analytes are thus expected to elute in the window between 40 and 70% of the column volume. (The size of the separation window equals the total pore volume in the column packing.) Each analyte must have a fixed position in this window corresponding to the portion of the pore volume that is accessible to its molecules. In analytical SEC, the hydrodynamic radius of a species thus can be directly read from the calibration plot showing the relationship between the analyte sizes and their elution volumes. Importandy, the distance between the elution volume of a totally excluded analyte and that of a small species of the size of a water molecule should not exceed the above one-third of the bed volume. This is the maximum separation selectivity that can be expected for the pure size exclusion mechanism of separation. 

The last part of the book, Chapters 10—17, reports on different applications of polymers in the field of analytical chemistry sorption of organic compounds, Hke phenols, pesticides or caffeine, the use of polymeric materials for size-exclusion chromatography, for HPLC packing materials or as solid phase extraction sorbents. The examples cover a broad variety of chemical compounds, fike pesticides, pharmaceuticals, organic acids in different matrices, such as food, biological fluids, non-aqueous media, air and the use of hemosorbents in blood purification. 

Divinylbenzene- or styrene-divinylbenzene-based packings were originally developed for the size-exclusion chromatography of industrial polymers (16). They are prepared via radical polymerization of the monomers. The monomers... 

Neutral hydrophilic polymeric packings are also useful for HILIC (6). Examples are the hydrophilic methacrylate phases, which were originally designed for aqueous size-exclusion chromatography. The surface of these packings consists of polyol groups, which are very hydrophilic. These phases tend to be more retentive than silica-based bonded phases. 

Suppliers of polymeric packings for aqueous size-exclusion chromatography are Polymer Labs (Plgel, UK), Showa Etenko (Shodex OHpak, Japan), Tosoh (TSKgel PW, Japan), and Waters (Ultrahydrogel, USA). 

Size Exclusion Chromatography (SEC) uses columns packed with a porous, inert material (with pore dimensions similar to the dimensions of the macromolecules to be analyzed) which does not interact with the polymer. The SEC method is based on the fact that when a polymeric solution is in the presence of a porous particle, smaller polymer molecules penetrate the pores more deeply than the larger ones. 

Because these crosslinked polystyrene beads have pore sizes that are controlled by suspension polymerization parameters and the crosslinking density of the polymer, they are being used as column packing materials for size-exclusion chromatography, also known as gel permeation chromatography (GPC). The crosslink density increases with increased divinyl benzene concentration. 

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