Immobilized stationary phases

S. Blomherg and J. Roeraade, Preparative capillary gas cliromatography. IF Fraction collection on rtaps coated with a very tliick-film of immobilized stationary phase , J. Chromatogr. 394 443-453 (1987). 

Geetha, T. Singh, S. Applications of immobilized stationary-phase hquid chromatography A potential in vitro technique. PSTT 2000, 3, 406 -416. 

The major disadvantages of the on-column injection approach are associated with drenching the column inlet directly with the introduced liquids, and a repeated deposition of non-volatile impurities. As a solution to the former problem, the development of immobilized stationary phases appears appropriate. However, removal of non-volatile sample impurities requires more judicious sample clean-up, a potential source of compound losses that may well counterbalance the advantages of the sampling method. While technical improvements are still needed, the on-column injection in capillary GC has undeniable advantages for the analyses of biological materials. 

Polymer encapsulated sorbents have been prepared by peroxide-induced or ozone-induced free radical crosslinking of coated porous silica or diatomaceous supports at elevated temperatures [175]. By reloading and performing sequential crosslinking reactions up to 20% (w/w) of liquid phase can be immobilized over the support surface. This reaction is analogous to the widely used procedure for immobilizing stationary phases in open tubular colunms. Few practical applications have been demonstrated. 

Figare 2j6 Mass transfer in a capillary with an immobilized stationary phase. designates the mass transfer in the mobile phase, and Cg designates the mass transfer in the stationary phase. 

Jindal, R. and Cramer, S.M., On-chip electrochromatography using sol-gel immobilized stationary phase with UV absorbance detection, Journal of Chromatography A, 1044, 277-285, 2004. 

However-well the column may be coated, the stability of the column depends on the stability of the stationary-phase film, and thus on the constant namre of the surface tension forces holding it to the column wall. These surface tension forces can change with temperature or be effected by the samples used for analysis. As a consequence, the surface tension can be suddenly reduced and the film break up. It follows that the stationary phase should be bonded in some way to the column walls or polymerized in situ. Such coatings are called immobilized stationary phases and cannot be removed by solvent washing. 

Chiral ligand exchange chromatography can be performed either on an achiral stationary phase with a chiral mobile phase or on a chiral stationary phase IMAC is performed on the metal ion immobilized stationary phase. The latter two stationary phases may be symbolized by the same formula as... 

One important feature of a capillary column is the possibility of its use without a splitter to eliminate sample discrimination and to improve analytical characteristics. Therefore in the past few years chromatographers gave preference to wide capillary columns with a thick (a few micrometers) layer of immobilized stationary phase (see, e.g., [15, 16]). 

In WC OTcolumns, the stationary phase, which is a silicone or polyethylene glycol, is either mechanically distributed on the wall or immobilized, either by binding the stationary phase chemically to the wall or by polymerization of the stationary phase into a nonextractable rubber (or both). Columns with immobilized stationary phase have increased stability and lifetime and are now most common in use. 

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