The resolution of ibuprofen enantiomers was conducted on a chiral stationary phase of Kromasil CHI-TBB column (250 mm×4.6 mm I.D.,5 μm,Eka Chemicals AB, Bohus, Sweden).The thermodynamic properties of the enantiomers in supercritical/subcritical fluid chromatography were investigated in the ranges of 293—323 K and 12.0—21.0 MPa,and compared with those in high performance liquid chromatography in the range of 288—328 K.The mobile phases were isopropanol/carbon dioxide (2∶98, by mass), 690.0 ml·min -1 (at ambient temperature and pressure), and isopropanol/hexane (3∶97, by volume),2.0 ml·min -1,respectively.The plots of lnk′ and lnα versus 1/T were straight lines in HPLC.The plots of lnα versus 1/T were still straight lines but the linear relationship of lnk′ versus 1/T could not be observed in SFC. The differences of enthalpy changes and entropy changes for the transfer of enantiomers from the mobile phase to the stationary phase were calculated.In both cases,｜Δ R,SΔH0｜>｜TΔ R,SΔS0｜, therefore,the enthalpic contribution to the overall enantiomer transfer energy is more important than the entropic contribution in the temperature range examined, and furthermore, lower temperature is better for chiral resolution of ibuprofen.
