Stationary phases crosslinking

Virtually all current research in SFC utilizes either small bore packed columns with particles of 5-10 micrometers in diameter optimized for use in liquid chromatography or narrow bore, fused silica open tubular columns with Immobilized phases similar to those used in gas chromatography. In the latter case columns of saaller internal diameter, 10-100 micrometers, shorter lengths (generally less than 20 m with 1-10 m being the most common length), and more firmly crosslinked stationary phases are used by coaparison with standard columns for gas chromatography. In all... 

Deactivation procedures and crosslinked stationary phases 1983 Megabore column introduced as an alternative to the packed column... 

An alternative approach to stationary phase immobilization, and the most popular method in contemporary practice, is the free radical crosslinking of the polymer chains, using peroxides [201,202,245-248], azo-oospounds [202,249-251], ozone [252], or gamma radiation [253-255] as free radical generators. In this case, crosslinking occurs through the formation of (Si-C-C-Sl) bonds as shown below ... 

Non-silica-based RP-HPLC stationary phases have also been developed and their separation capacity has been compared with those of silica-based ones. The porous structure of crosslinked polymer gels may be responsible for the markedly different selectivity and retention characteristics. Up till now, the mode of separation on polymer stationary phases is not entirely understood at the molecular level. It has been established that the size-exclusion effect may influence the retention of analyses on polymer gels. 

In a GPC experiment, the polymer is separated in a column which is filled with a swollen, uniformly packed resin ( gel , called stationary phase, while the solvent which passes through the column is called mobile phase). The gel beads are usually made of crosslinked polymers (in particular polystyrene but also various inorganic porous materials) with little holes and pores of different size where the pore diameter is of the dimension of the size of the solvated polymer coils, i.e., the pore-size distribution is approx. 10-10 nm. 

Different capillary columns are available for organic acid separation and analysis. In our laboratory, the gas chromatography column in all GC-MS applications is crosslinked 5% phenyl (poly)methyl silicone, 25 m internal diameter 0.20 mm stationary phase film thickness 0.33 pm (Agilent HP-5, DB-5, or equivalent). Several instrument configurations are commercially available, which allow for positive identification of compounds by their mass spectra obtained in the electron impact ionization mode. A commercially available bench-top GC-MS system with autosampler (Agilent 6890/5973, or equivalent) is suitable. Software for data analysis is available and recommended. The use of a computer library of mass spectra for comparison and visualization of the printed spectra is required for definitive identification and interpretation of each patient specimen. 

Support materials for solid phase extraction (SPE) and for chromatographic techniques have been prepared by ROMP. pH-stable high capacity stationary phases have been prepared by copolymerization of functional monomers with a suitable crosslinking agent, with precipitation polymerization techniques. 

J. Hubbal, P. MiDauro, et al., Developments in crosslinking of stationary phases for capillary gas chromatography by cobalt-60 gamma radiation, J. Chromatogr. Sci., 22 185-191 (1984). 

Coating the inside of a capillary tube requires pretreatment of the silica so that the liquid will wet the surface and stick to it.1112 Stable stationary phases have been attained recently by bonding the liquid to the silica and/ or crosslinking it, using a variety of methods including gamma irradiation.13 The crosslinked bonded phase OT columns are very stable and can even be washed with (liquid) solvents for cleaning. 

The selection and chemical modification of the current generation of chemically and physically robust stationary phases with narrower particle and pore size distributions has been based on the developmental effort that has occurred over the past 20 years. Initially chemically modified, deformable polymeric gels were used, such as the crosslinked agaroses, dextrans, or acrylate-based copolymers, but more recently various classes of highly refined type I and type II silicas and other ceramic materials, or new classes of controlled porosity polymeric organic materials have found increasing application. 

Covalently bound templates have been extensively studied from 1972 [27, 28] up to the present day by Wulff et al. [62-64] who were joined by Damen and Neckers (1980) [65,66], by Sarhan et al. (1982) [67-69] and by Shea and Thompson (1978) [70]. A variety of parameters have been investigated and their influence on the selectivity of binding and the application of these polymers as chiral stationary phases have been quantified. The parameters investigated are the degree of crosslinking [65,66,71-79] the structure of the crosslinker [71,72,... 

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