SFC vs. Other Column Methods

As shown in Table 13.4, several physical properties of SCFs are intermediate between gases and liquids. Hence, SFC combines some of the characteristics of both GC and LC. For example, like GC, SFC is inherently faster than LC because of the lower viscosity and higher diffusion rates in supercritical fluids. High diffusivity, however, leads to band spreading, a signiflcant factor with GC but not with LC. The intermediate diffusivities and viscosities of supercritical fluids result in faster separations than are achieved with LC together with lower band spreading than encountered in GC. 

In Section 11.4 we described the mechanism of the chromatographic separation process using an extended analogy to people stepping on and off a moving slideway. We mentioned that if different classes of people stayed always on the slideway but walked forwards or backwards at different constant rates they would separate themselves along 

---