Page 149 - Multidimensional Chromatography

Coupled Supercritical Fluid and Chromatographic Techniques 141

Figure 6.5 Schematic diagram of a typical interface used for on-line SFE–GC coupling
(from ref. 40): 1, extraction cell; 2, restrictor; 3, on-column injector; 4, heater; 5, oven; 6,
cryogenic module; 7, column.

6.5 SFE–SFC

The on-line coupling of supercritical fluid extraction with Supercritical Fluid
Chromatography (SFE–SFC) is easier to achieve than those involving other chro-
matographic techniques. This is particularly the case when using neat CO 2 in both
systems since it does not requires changes in the fluid composition or physical state.
The SF extracts will contain the extracted analytes in CO 2 and these can be directly
transported into the SFC system, which also uses CO 2 as the mobile phase. Different
approaches have been used to trap and focus the analytes into the SFC column
(26, 27), including a dual-trapping system to eliminate the modifier solvent (41).
Figure 6.7 shows a schematic diagram of an on–line SFE–SFC coupled system
(42), with details of the interface being shown in Figure 6.8 (42).

6.6 SFE-LC

Unfortunately, not much experimental work has been carried out on the combination
of supercritical fluid extraction and liquid chromatography systems (43, 44). One of
the reasons for this arises from the difficulties in achieving compatibility between
the extraction solvent and the LC mobile phase. Baseline perturbations have been