Effects of trace water in mobile phase on enantioseparation of α-propionate derivatives in normal phase chromatography
Xia, T.; Zhang, X.; Gu, F.; Chen, J.; Cai, X.
Se Pu 29(12): 1188-1193
2011
ISSN/ISBN: 1000-8713 PMID: 22500445 Document Number: 655228
Trace water was added as a modifier of the mobile phase to achieve enantioseparation of alpha-propionate pollutants and their degradation products in normal phase high performance liquid chromatography (HPLC). A Chiralcel OJ-H column (25 cm x 4.6 mm, 5 microm) was used with hexane-isopropanol-acetic acid as the mobile phase. The flow rate of the mobile phase was 0.8 mL/min. The results indicated that the addition of trace water differentially improved enantiomeric resolution of chiral alpha-propionate compounds, depending on the amount of water added and chemical structure of the analytes. It is primarily ascribed to the fact that trace water bound to chiral stationary phase and competed with the analytes. Moreover, trace water affected pH values of the mobile phase and the dissociation of free acids, thereby induced the variation in resolution efficiency. Additionally, the free acids were more sensitive to trace water than their neutral analogues (i. e., amides and carboxylic esters), in terms of the different roles of enthalpy and entropy terms.