ABSTRACT
I. INTRODUCTION AND HISTORICAL PERSPECTIVE The role of supercritical fluid media, or ' 'critical" fluid technology (which also includes the near critical state) in analytical separation science developed from several diverse sources, originating as a hybrid technique of gas chromatography in the mid-1960s. The most often cited origins of supercritical phenomena are from phase equilibria studies or geochemical processes conducted at high pressures and temperatures [1]. Interest in this particular ''intermediate state" of matter also found early application in petroleum recovery [2], which was followed by pioneering research in the late 1960s on applying supercritical fluids for the extraction of solutes (e.g., caffeine) and as a versatile reaction medium (polymerizations, hydrogénations). In parallel with this latter trend was the observation that chromatographic retention parameters were effected by column pressure when utilizing nonideal fluids such as carbon dioxide as eluents. This gave rise to a different form of gas chromatography called "dense gas chromatography" [3], which permitted intractable solutes of limited volatility to be solubilized in the mobile phases and separated as a function of eluent pressure or density.
