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 embedd ed in the anchored alkyl chain. The retention times of strongly basic solut es on such phases are much shorter than on conventional RP columns, and the y are eluted with symmetrical peaks. The polar embedded groups, usually ami de or carbamate groups, contribute to the retention of polar solutes; thus, e.g. analytes with phenolic groups are much more strongly retarded on shie lded RP columns. This polar selectivity is shown to improve the separation of the dinitrophenylhydrazones of C-3 aldehydes and ketones and result in b etter selectivity in the determination of flavonoids in wine. Different sel ectivities for classical RP columns and shielded phases with methanol and a cetonitrile as organic modifiers are demonstrated.