The Phase Diagram View of Chromatography

We must start with fluid behavior to understand the basic concepts of unified chromatography. We must forget most of what we know from common experience about liquid and gas behavior since this experience is tied with ambient conditions. Instead, we must embrace the new possibilities afforded by temperatures and pressures that are different from ambient. This new view requires phase diagrams (17, 18). 

we should ask ourselves about the properties of water in this continuum of behavior mapped with temperature and pressure coordinates. First, let us look at temperature influence. The viscosity of the liquid water and its dielectric constant both drop when the temperature is raised (19). The balance between hydrogen bonding and other interactions changes. The diffusion rates increase with temperature. These dependencies on temperature provide uS with an opportunity to tune the solvation properties of the liquid and change the relative solubilities of dissolved solutes without invoking a chemical composition change on the water. 

there is not necessarily a boundary at the normal boiling point when we control the pressure. Why would we not want to take full advantage of the full range of properties of water, or of any other solvent, whenever advantages discovered away from ambient conditions improve our ability to separate solutes of interest  

The shaded region is that part of the phase diagram where liquid and vapor phases coexist in equilibrium, somewhat in analogy to the boiling line for a pure fluid. The ordinary liquid state exists on the high-pressure, low-temperature side of the two-phase region, and the ordinary gas state exists on the other side at low pressure and high temperature. As with our earlier example, we can transform any Type I mixture 

LC is a limiting technique that occurs when the column outlet pressure is near ambient and we choose well-behaved liquids as our mobile phases. Our only means of adjusting solute retention (after selecting the stationary phase and the 

---