Chemically bonded phases polymeric

The influence of the bonded organic moiety on solute retention has not yet been elucidated and only a very small number of papers discuss the properties and use of such phases so far. The numerous advantages of chemically bonded phases make the application of polar chemically bonded phases with nonpolar eluents quite attractive even if the standardization of these phases may pose problems 106) similar to those encountered in the standardization of aidsorbents as well as of polymeric liquid phases in gas chromatography. A detailed discussion of the properties and chromatographic use of bonded stationary phases is given by Melander and Horvath (this volume). 

The mechanism of ion polymerization in formaldehyde crystals proposed by Basilevskii et al. [1982] rests on Semenov s [1960] assumption that solid-phase chain reactions are possible when the arrangement of the reactants in the crystal prepares the configuration of the future chain. The monomer crystals capable of low-temperature polymerization fulfill this condition. In the initial equilibrium state the monomer molecules are located in the lattice sites and the creation of a chemical bond requires surmounting a high barrier. However, upon creation of the primary dimer cation, the active center shifts to the intersite, and the barrier for the addition of the next link... 

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. 

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).

Stationary phase Chemically bonded silica, alumina, polymeric resins Polysiloxanes... 

A final important reproducibility specification should be considered which applies specifically to bonded-phase packings. First, the bonded-phase should be specified as being polymeric or monomeric. If polymeric,information on the % organic or % carbon for the packing and the chemical structure of the bonded phase should be provided. However, as shown before, this information is often not sufficient to determine lot-to-lot chromatographic reproducibility. If the bonded phase is monomeric, data on the % organic or % carbon and chemical structure are also useful, but in addition, the surface coverage calculated from these values (6) should also be provided (EQ. 4). 

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