QUANTITATIVE STRUCTURE-RETENTION RELATIONSHIPS FOR SECONDARY INTERACTIONS IN CATION-EXCHANGE LIQUID-CHROMATOGRAPHY

Eighty-three aryl alkyl amines with a range of substituents in the aromatic ring were chromatographed on a silica stationary phase in the ion-exchange mode using a non-polar eluent which promotes hydrogen bonding interactions. The increase in retention due to the presence of the polar substituents was quantified using the functional group contribution value tau. The correlation between tau and a range of substituent physical and quantum chemical parameters was investigated using multiple regression. The increase in retention could be attributed to a hydrogen bonding interaction between the polar substituents and unionised silanols. This could be quantified in terms of the hydrogen bonding acceptor properties of the substituent (log K-beta) and it size, although the quality of the correlations was poor. A superior correlation was obtained using the lipophilicity (pi) of the substituent. The correlations, which gave an R(2) of 0.8423 at best were unsuited to accurate retention prediction.