Bonded phases polymeric

The above data were obtained on a polymeric bonded phase and not a brush phase. The so-called brush phases are made from monochloro-sxlants, (or other active group) and, thus, the derivative takes the form of chains attached to the silica surface [2]. The bulk phases are synthesized from polyfunctional silanes in the presence of water and, thus, are cross linked and form a rigid polymeric structure covering the silica surface. These two types of phases behave very differently at low concentrations of moderator. 

In contrast, the alkane chains on the polymeric phase cannot collapse in an environment of water as they are rigidly held in the polymer matrix. Thus, the retention of the solute now continuously falls as the methanol concentration increases as shown in Figure 4. It should be pointed out that if the nature of the solutestationary phase interactions on the surface of a bonded phase is to be examined in a systematic manner with solvents having very high water contents, then a polymeric phase should be used and brush type reversed phases avoided if possible. 

The other restriction of SynChropak size exclusion columns is a general one for silica-based supports, that of pH. The most harmful pH is that above 7.5 due to silica dissolution. The bonded phase of SynChropak GPC has some polymeric properties therefore, it is not removed rapidly from the silica at pH 2-3. The bonded phase of SynChropak CATSEC is polymeric and stable at pH 2-7.5. 

The use of bonded, silica column supports has also become a useful way to characterize cationic, water-soluble polymers. CATSEC SEC columns from Micra Scientific contain a silica support with a polymerized polyamine-bonded phase. This imparts a cationic surface charge on the packing that can be... 

Bonded-phase chromatography (BPC). To overcome some of the problems associated with conventional LLC, such as loss of stationary phase from the support material, the stationary phase may be chemically bonded to the support material. This form of liquid chromatography, in which both monomeric and polymeric phases have been bonded to a wide range of support materials, is termed bonded-phase chromatography . 

The above results proved the potential viability of the adsorbed hydrophilic macromolecules as bonded phases in chromatography of biopolymers but it must be admitted that additional crosslinking of previously adsorbed macromolecules is usually needed in order to obtain stable composites. The cross-linked bonded polymeric phases, however, may suffer from the restricted flexibility of the chain segment and their steric repellency may be diminished. Moreover, the conformational adaptivity of cross-linked chains for binding with solutes is poorer than that of grafted or chemically bound macromolecules. 

Indeed, the polymeric interface seems to be highly diffuse and hydrophilic because copolymers of N-vinylpyrrolidone and N- (2-hydroxyethyl) acrylamide are readily soluble in water [53]. Besides, aminopropyl-glass adsorbs the acryloyl chloride copolymer so that only 10% of its active functions become amidated. The rest is located on the loops and tails of the attached macromolecules [51]. Thus the steric repulsion of the bonded phase is a probable reason for the high inertness of the packing towards viruses. 

The polymeric resin beads fill a need that arises from the instability of silica gel and its products to mobile phases of extreme pH (outside a pH range of about 4.0-7.0) and, consequently, are employed in most ion exchange separations. Organic moieties containing ionic groups can be bonded to silica and produce an effective ion exchange media, but the restrictions of pH on phase stability still apply. It follows that ion exchange bonded phases are less popular than the polymer bead alternatives. 

Figure 4.3 Synthesis of onoaeric and polymeric siloxane bonded phases by reaction of organochlorosilanes with silica gel under different conditions.

Figure 4.4 Separation of SRM 1647 and SRH 869 polycyclic aromatic hydrocarbon test mixtures on a monomeric and polymeric reversed-phase octadecylsiloxane bonded phases by gradient elution. (Reproduced with permission from ref. 69. Copyright American Chemical Society).

Fig. 3.2a. Preparation of bonded phases. Reaction of silica with substituted chlorosilanes to form (i) monomeric (ii) polymeric...

More complicated surface structures can be produced by changing the functionality of the silylating agent and the conditions under which the reaction is carried out. The use of di- or trichlorosilanes in the presence of moisture can produce a crosslinked polymeric layer at the silica surface, as shown in Fig. 3.2a (if). Monomeric bonded phases are preferred, as their structure is better defined and they are easier to manufacture reproducibly than the polymeric materials. 

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