Chapter 7: Supercritical Fluid Chromatography

Overview

Unlike paper and thin-layer chromatography (TLC; Chapters 5 and 6) techniques in which very little new work has been published since the 1970 s, supercritical fluid chromatography (SFC) is a rapidly expanding area.

Until recently the chromatographer has had to rely on either gas chromatographic (GC) or high performance liquid chromatography (HPLC) for separations, enduring the limitations of both [1]. Lee Scientific has created a new dimension in chromatography, one which utilises the unusual properties of supercritical fluids. With the new technology of capillary supercritical fluid chromatography (CSFC) the chromatographer benefits from the best of both worlds - the solubility behaviour of liquids and the diffusion and viscosity properties of gases. Consequently, CSFC offers unprecedented versatility in obtaining high-resolution separations of difficult compounds.

Beyond its critical point, a substance can no longer be condensed to a liquid, no matter how great the pressure. As the pressure increases, however, the fluid density approaches that of a liquid. Because solubility is closely related to density, the solvating strength of the fluid assumes liquid-like characteristics. Its diffusivity and viscosity, however, remain. SFC can use the widest range of detectors available to any chromatographic technique. As a result, CSFC has already demonstrated a great potential in application to polymer additives.

SFC is now one of the fastest growing analytical techniques. The first paper on the technique was by Klesper and co-workers [2], but SFC did not catch the analyst s attention until Novotny and co-workers [3] published the first paper on CSFC.

Most supercritical fluid...