The road to unified chromatography: The importance of phase behavior knowledge in supercritical fluid chromatography and related techniques, and a look at unification

In supercritical fluid chromatography (SFC) and related techniques, and in chromatography in general, knowledge of phase behavior is essential to unde rstand mass transfer throughout the process. Complete three-dimensional pha se diagrams of binary fluids including CO2 are both rare and difficult to u se. However, much of the information necessary for chromatography is contai ned in two-dimensional projections of the critical loci of binary mixtures. When CO2 is one of the fluid components, we are able to quickly produce th ese projections in the laboratory using a peak-shape-sensitive flow-injecti on procedure based on SFC equipment. The importance of the phase behavior k nowledge gained is illustrated with examples of sample injection in open-tu bular SFC and detector interfacing in packed-column SFC when the detector i s operated at a different temperature and pressure than the column outlet. Knowledge of the phase behavior of chromatographic mobile phases also leads us to new possibilities for control of selectivity and shortening of analy sis times by making use of temperatures and pressures that are off limits i n conventional gas (GC) and liquid (LC) chromatography. This leads us to a unified view of chromatography in which parameters can be varied continuous ly as long as we remain in the one;phase region of the phase diagram. In th is view, conventional GC and LC become limiting cases of the more general d escription. (C) 1999 Academic Press.