Pellicular materials

Pellicular materials consist of a solid spherical bead of relatively large... 

The different stationary phases can also be classified on the basis of their physical structure. Pellicular materials, the particles of which consist of a hard (glass) core covered by a thin layer of an ion-exchange resin, may be used if a moderate efficiency and a small ion-exchange capacity are acceptable, but not if the column is required to have a high... 

As an alternative to pellicular materials, microparticulate stationary phases may be used. These are either based on organic resins or on inorganic oxides. The latter class contains bare oxides, as well as chemically bonded phases, which may be synthesized in a way similar to that described in section 3.2.2.1, but the functional end group is now an ionic one. 

Guard columns may be filled either with pellicular material (see Fig. 3-13) of the same bonded phase as the analytical column or with the identical packing material as in the analytical column. Pellicular packings (35-40 /urn)... 

Kennedy and Knox [274] compared the performances of Porasil, Corasil, Corning Porous Glass and Zipax for retained and unretained organic solutes. The performance of Zipax and the efficiency of columns of different particle size have been studied [275]. The performance of Permaphase ETH and Permaphase ODS, pellicular materials consisting of silicones bonded to silica, has also been investigated [276]. 

Fig. 8.5. Separation of ellipticine and related alkaloids, isolated from mouse blood Column"yBondapak C18 (300x4.0 mm ID), protected with a precolumn (50x4.6 mm ID) packed with a 40 urn pellicular material, mobile phase acetonitrile - 0.01 M sodium dihydrogen phosphate (1 3)(pH 3.5 with 2 N phosphoric acid), flow rate 1.4 ml/min, detection UV 300 nm. Peaks 1, ellipticine 2, 9-hydroxyellipticine 3, 11-demethylellipticine (internal standard).

There are two distinct types of silica resins. Totally porous resins have a quaternary ammonium functional group chemically attached. Their particle size is in the range of 3 pm to 10 pm with typical exchange capacities of 0.1 to 0.3 mequiv/g. Pellicular materials have a larger particle size and are covered with a thin layer of a polymer with quaternary ammonium groups. For example, Zipax SAX is covered with a layer of lauryl methacrylate 1 pm to 3 pm thick. 

The HPLC of large biomolecules such as proteins and DNA often requires specialized columns packed with wide-pore polymer or silica-based bonded phase with extra-low silanol activity.1215 Alternate approaches are pellicular materials or very small nonporous particles. Some of these columns are packed in PEEK or titanium hardware to allow the use of high-salt mobile phase and to prevent possible protein denaturing by metallic leachates. Further details on bio-separations and application examples are discussed in Chapter 7. 

A material. Note that wide-pore packings typically have lower surface area and therefore lower sample capacities. Other approaches for bioseparations are the use of very-wide-pore materials,34 45 nonporous,35 or pellicular materials (Figure 7.26). Nonporous and pellicular materials are particularly useful for fast separations. 

On ion-exchange resins the rate of diffusion through the stationary phase, to and from the ion-exchange site, is relatively slow. This slow mass transfer results in a large contribution towards band broadening. Pellicular materials with only a thin layer of resin were evolved to... 

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