The polar selectivities of non-polar reversed phases

To reduce the influence of surface silanol groups on the retention of basic solutes reversed phases (RP) have been introduced with polar groups embedded in the anchored alkyl chain. The retention times of strongly basic solutes on such phases are much shorter than on conventional RP columns, and they are eluted with symmetrical peaks. The polar embedded groups, usually amide or carbamate groups, contribute to the retention of polar solutes; thus, e.g. analytes with phenolic groups are much more strongly retarded on shielded RP columns. This polar selectivity is shown to improve the separation of the dinitrophenylhydrazones of C3 aldehydes and ketones and result in better selectivity in the determination of flavonids in wine. Different selectivities for classical RP columns and shielded phases with methanol and acetonitrile as organic modifiers are demonstrated.