Supercritical fluid chromatography discussion

Supercritical fluid chromatography employs supercritical fluid instead of gas or liquid to achieve separations. Supercritical fluids generally exist at conditions above atmospheric pressure and at an elevated temperature. As a fluid, the supercritical state generally exhibits properties that are intermediate to the properties of either a gas or a liqiud. Chapter 16 discusses various advantages of SFC over GC and HPLC and also provides some interesting applications. 

In supercritical fluid chromatography, fluids above their critical point are used as mobile phases. This chapter discusses the principles of operation, mobile phase considerations, parameters that can be adjusted in method development as well as an overview of instrumentation required and a few pertinent examples from current literature. Not everything can be illustrated, but the advantages of this diverse technology will be highlighted. 

Enantioselective separation by supercritical fluid chromatography (SFC) has been a field of great progress since the first demonstration of a chiral separation by SFC in the 1980s. The unique properties of supercritical fluids make packed column SFC the most favorable choice for fast enantiomeric separation among all of the separation techniques. In this chapter, the effect of chiral stationary phases, modifiers, and additives on enantioseparation are discussed in terms of speed and resolution in SFC. Fundamental considerations and thermodynamic aspects are also presented. 

Discusses the increase in speed of enantiomeric separations using supercritical fluid chromatography... 

The CHEMISTRY OF SUPERCRITICAL FLUIDS has been studied extensively in the past decade. Consequently, our understanding of this field has expanded significantly. Simultaneously, the number of applications in associated analytical technologies (for example, supercritical fluid chromatography and supercritical fluid extraction) has increased. Although the areas of fundamentals and applications are clearly interrelated, they are often discussed separately. 

The complicated dependence of retention in supercritical fluid chromatography as a function of temperature and pressure is examined. Simple thermodynamic relationships are derived and discussed which allow the calculation of the slope of solute retention as a function of both temperature and pressure. 

Wall [17] has discussed recent developments including timed-split injection, extraction and detection systems in supercritical fluid chromatography. 

It is also possible to employ detectors with solutions flowing over a static mercury drop electrode or a carbon fiber microelectrode, or to use flow-through electrodes, with the electrode simply an open tube or porous matrix. The latter can offer complete electrolysis, namely, coulometric detection. The extremely small dimensions of ultramicroelectrodes (discussed in Section 4.5.4) offer the advantages of flow-rate independence (and hence a low noise level) and operation in nonconductive mobile phases (such as those of normal-phase chromatography or supercritical fluid chromatography). 

Various methods of detection are employed in chromatography. Each approach for the detection of solutes is based on their physical or chemical properties. Some of the more commonly used detectors are discussed here for liquid chromatography (LC), gas chromatography (GC), and supercritical fluid chromatography (SEC). 

Characterization in the solid-state and compendial methods has been discussed already. Quantitative tests to characterize drug substance and drug product composition require that significant consideration be given to method development. Methods such as thin layer chromatography, gas chromatography, HPLC, supercritical fluid chromatography, and capillary electrophoresis... 

Supercritical fluid chromatography has at least one extra control variable compared to HPLC. Many people still associate the name SFC with syringe-pump-based systems in which pure carbon dioxide was used with pressure programming. Modern SFC sometimes still operates in this manner but only for nonpolar solutes. SFC is somewhat different from HPLC. It is useful to discuss the relative effects of different control variable on retention and selectivity. The relative effects of several control variables are represented schematically in Fig. 5. 

Of these, capillary GLC and HPLC are providing the main thrust In ultrahlgh resolution chromatography. Supercritical fluid chromatography Is opening some new avenues and, hopefully, will provide resolution that Is not possible now with GLC or HPLC. Hence, mainly these subjects have been covered In this book. Whereas, some Improvements In resolution have been obtained with HPTLC, further Improvements are possible In the area of detection and quantification. Ultrahlgh resolution with the other modes of separation still remains within the domain of a handful of experts. Some Information Is Included on these under Miscellaneous techniques, however, a detailed discussion of these techniques Is deferred to a future symposium. 

High Performance Liquid Chromatography (HPLC), Gas Chromatography (GC) and Supercritical Fluid Chromatography (SFC), and Electrophoresis, are topics covered in details in Chapters 2, 3, and 9, respectively. Consequently, they are not discussed further in this chapter. 

The discussion of supercritical fluid chromatography given above may be concluded by highlighting the distinct usefulness of this technique. 

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