Retention Prediction and Hydrophobicity Measurement of Weakly Basic Compounds in Reversed-phase Liquid Chromatography Using Ammonia and Triethylamine as Ion-suppressors

Abstract

The purpose of this study is to investigate the retention behavior of weakly ionizable basic compounds in ionsuppression reversed-phase liquid chromatography (IS-RPLC) using ammonia or triethylamine as ion-suppressor in a binary hydroorganic mobile phase. The apparent n-octanol-water partition coefficient (Papp) was proposed to adjust the noctanol- water partition coefficient (Po/w) of weakly basic compound. LogPapp was found to have a better linear correlation with logkw, the logarithm of hypothetical retention factor corresponding to neat aqueous fraction of the mobile phase. This straightforward relationship has been applied to effective prediction of retention behavior of weakly basic compounds, and offered a promising medium for direct determination of Po/w data for these solutes. In addition, the relationship between mobile phase pH and retention behavior of weakly basic compounds was studied in this IS-RPLC mode, and the possible reasons for the biphasic effect of pH on retention have been explained. Keywords: Ion-suppressor, n-Octanol-water partition coefficient (Po/w), retention behavior, reversed-phase liquid chromatography, weakly ionizable basic compound.