Page 145 - Multidimensional Chromatography

Coupled Supercritical Fluid and Chromatographic Techniques 137

Figure 6.2 Schematic diagram showing the basic components of (a) SFE and (b) SFC
instruments: 1, carbon dioxide; 2, high pressure pump; 3, oven; 4, extraction cell (SFE) or col-
umn (SFC); 5, collection vial (SFE) or data system (SFC).

Although SFE and SFC share several common features, including the use of a
supercritical fluid as the solvent and similar instrumentation, their goals are quite
distinct. While SFE is used mainly for the sample preparation step (extraction), SFC
is employed to isolate (chromatography) individual compounds present in complex
samples (11–15). Both techniques can be used in two different approaches: off-line,
in which the analytes and the solvent are either vented after analysis (SFC) or col-
lected (SFE), or on-line coupled with a second technique, thus providing a multidi-
mensional approach. Off-line methods are slow and susceptible to solute losses and
contamination; the on-line coupled system makes possible a decrease in the detec-
tion limits, with an improvement in quantification, while the use of valves for
automation results in faster and more reproducible analyses (16). The off-line