Polar-embedded group bonding

Polar-Embedded Groups—The incorporation of a polar group (e.g., carbamate, amide, urea, ether, sulfonamide) in the hydrophobic chain of the bonding reagent has led to a new class of popular phases with different... 

The polar groups are, on the other hand, responsible for an induced polar selectivity. Analytes able to form hydrogen bonds like phenols are retarded more strongly with polar-embedded stationary phases than with the corresponding classical RP of an identical carbon content. This is demonstrated in Figure 2.5 for the separation of polyphenolic compounds present in red wine. The retention time of the polyphenolic compound kaempferol with the shielded phase is more than three times longer than with the corresponding RP column of an identical carbon content. The polar... 

Use of alkylamide phases, in which alkyl chains are attached to the silica surface via an alkylamide group, reduces interactions with free silanols, by an internal masking mechanism. Residual silanols interact by hydrogen bonding with the embedded amide groups and thus become less active toward analytes. The embedded polar amide groups lessen the hydrophobicity of these phases compared to that of C18 bonded phases prepared from the same silica. Improved peak shapes of ionizable compounds were reported and this stationary phase was successfully used under IPC conditions to analyze streptomycin and its dihydrostreptomycin derivative in food... 

The special phases with an embedded polar functional group are designed for reversed-phase chromatography. The polar function shields the silica surface, preventing the interaction of analytes with the acidic silanols on the silica surface. For many samples, they exhibit a significant difference in selectivity compared to simple hydrocarbon bonded phases. Also, the tailing of basic analytes is reduced. 

This hydrogen bonding capacity expressed by the polar selectivity is not limited to an increase in retention for phenols. Packings with embedded polar groups that excel in this feature also exhibit increased retention for analytes with other functional groups. Specifically, carboxylic acids at acidic pH and with acetonitrile as the organic modifier and compounds with sulfonamide functions at acidic and neutral pH exhibit significant... 

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