Role of solute hydrophobicity and charges in reversed-phase ion-pair liquid chromatography

Abstract

The Logarithm of capacity factor in RP-HPLC and solute charges have been selected as descriptors of solute hydrophobicity and electrostatic interaction respectively. It has been observed that the logarithm of capacity factors (ln k ip ′ ) for a solute with one, two and three negative charges in RP-IPC can be well correlated with the logarithms of capacity factors (ln kR p ′ ) in RP-HPLC and solute charges (ne). Both the solute hydrophobicity and solute charges with opposite sign to those of the ion-pair reagent made a positive contribution to retention in RP-IPC. The logarithm of capacity factor linearly decreases with organic modifier concentration (Cb) and the logarithm of the inorganic salt concentration (lnCs). The intercept (ln k ip ′ , A) and slope (cip,B) values of a linear relationship between ln kR p ′ vs. Cb and ln k ip ′ vs. ln C5 also can be well correlated with ln kR p ′ and ne. The solute hydrophobicity and solute charges also made a positive contribution to the parameters ln k ip w and A, but a negative contribution to parameter cip. The parameter B, however is mainly determined by the solute charges.