Stationary phases inorganic oxides

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. 

Materials with inorganic or porous hydrophobic or (less frequently) hydrophilic organic polymer matrices and graphitized carbon are stable over a broad pH range from 0 to 12-14 hence, they are useful for separations of basic compounds. RP phases on aluminium and zirconium oxide supports exhibit hardness and mass transfer properties comparable to silica, and can be prepared by forming a cross-linked polystyrene, polybutadiene, or alkylated polymethylsiloxane layer on the support surface to which alkyls are attached. The inorganic surface, encapsulated by a nonpolar stationary phase, does not come into contact with the mobile phase or with the analyte, so these materials can be used in the pH range 1-14. 

Figure 6.13. Separation mode selection guide for TLC. LSC = liquid-solid chromatography on an inorganic oxide adsorbent BPC = liquid-solid chromatography on a chemically-bonded sorbent RPC = reversed-phase chromatography with a water-containing mobile phase and chemically-bonded stationary phase IPC = ion-pair chromatography with reversed-phase separation conditions and PC = precipitation chromatography. (From ref. [151] Elsevier)...

The chemical composition of sol-gels is typically a basic inorganic oxide. A common example of a sol-gel is silica gel, which has particular utility as stationary phase supports in chromatographic columns. The sol-gel materials used for electrode modification are typically created from two different classes of material inert and redox active. Many different types of sol-gels are derived from these classes, as outlined in Table 8.7 (113). 

Epoxidized PBD is also useful for grafting PBDs onto inorganic surfaces such as silica, alumina, and ferric oxide [206-210]. These PBD-modified materials exhibit, for example, good separation properties as the stationary phase in liquid chromatography [211]. Subsequent treatment with neat PBD or in the presence of silica with hydrochloric acid allows crosslinking of the remaining epoxide entities in PBD and formation of diether or a-hydroxyl ether entities [212,213]. Also, amine-terminated... 

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