A novel liquid chromatographic system which enables high temperature ultrafast liquid chromatography (HTU-FLC) has been designed through the careful consideration of heat transfer, band broadening, and pressure drop. Studies of the effect of linear velocity on the HETP show that column efficiency at high velocity, especially of well-retained solutes, dramatically improves at higher temperatures. At 150 degrees C, at a flow rate of 15 mL/min with a 5 cm by 4.6 mm (i.d.) column packed with 3 microns polystyrene-coated zirconia porous particles, long chain alkylphenones were completely resolved, and the analysis time could be decreased by a factor of 50 compared to that at room temperature (25 degrees C) at a conventional flow rate (4 mL/min). In addition, using pure water as the mobile phase, five phenols were separated in less than 30 s.

This review explores the usefulness of zirconia‐based materials in separations in biotechnology. The physical and chemical properties of zirconia are discussed briefly to familiarize the reader with the advantages of zirconia. The use of native zirconia is then examined, with a study of the Lewis acid/base chemistry that defines chromatography with zirconia. Modification of the zirconia surface with small molecules is then discussed. Finally, polymer‐coated zirconia materials are examined. Examples of separations using these various materials are shown. The advantages and disadvantages of each of these materials are presented.

Chiral separations depend upon column efficiency and chiral selectivity. Supercritical fluid chromatography (SFC) has been shown to have pronounced advantages in chiral separations due to its enhanced column efficiency at normal flow rates. Examination of factors affecting selectivity in SFC is crucial to systematic chiral method development. Selectivity is a compromise between differences in enantiomeric binding enthalpy and disruptive entropic effects. Increased temperature will decrease the effect of differences in enantiomer binding enthalpy, eventually decreasing selectivity to a point where the enantiomers coelute. Extension of this thermodynamic theory predicts that further increases in temperature lead to selectivity values of less than 1.0, and elution order of the enantiomers reverses. In this region separations are said to be "entropically driven", and selectivity increases (decreases from 1.0) with temperature. Performing separations in this region is attractive because column efficiency is also expected to increase with temperature. Such entropically driven separations have been observed only in gas chromatography. Most data used to support the application of this theory in SFC have been generated at subcritical temperatures, while theory purports to predict behavior above the critical temperature (T(c)). This approach ignores the effects of traversing the critical temperature in SFC, which is known to have a variety of unpredictable consequences. Work presented here shows the effect of temperatures above T(c) on chromatographic behavior. Contrary to theory, capacity factors increase near T(c) and column efficiency declines. Use of pressures well above the critical pressure lessens these effects. In accordance with theory, selectivity does decrease with temperature through T(c) and isoelution temperatures and two instances of elution order reversal are observed here for the first time in SFC.