Supercritical fluid chromatography analytical applications

A method which uses supercritical fluid/solid phase extraction/supercritical fluid chromatography (SE/SPE/SEC) has been developed for the analysis of trace constituents in complex matrices (67). By using this technique, extraction and clean-up are accomplished in one step using unmodified SC CO2. This step is monitored by a photodiode-array detector which allows fractionation. Eigure 10.14 shows a schematic representation of the SE/SPE/SEC set-up. This system allowed selective retention of the sample matrices while eluting and depositing the analytes of interest in the cryogenic trap. Application to the analysis of pesticides from lipid sample matrices have been reported. In this case, the lipids were completely separated from the pesticides. 

A number of analytical techniques such as FTIR spectroscopy,65-66 13C NMR,67,68 solid-state 13 C NMR,69 GPC or size exclusion chromatography (SEC),67-72 HPLC,73 mass spectrometric analysis,74 differential scanning calorimetry (DSC),67 75 76 and dynamic mechanical analysis (DMA)77 78 have been utilized to characterize resole syntheses and crosslinking reactions. Packed-column supercritical fluid chromatography with a negative-ion atmospheric pressure chemical ionization mass spectrometric detector has also been used to separate and characterize resoles resins.79 This section provides some examples of how these techniques are used in practical applications. 

In analytical chemistry there is an ever-increasing demand for rapid, sensitive, low-cost, and selective detection methods. When POCL has been employed as a detection method in combination with separation techniques, it has been shown to meet many of these requirements. Since 1977, when the first application dealing with detection of fluorophores was published [60], numerous articles have appeared in the literature [6-8], However, significant problems are still encountered with derivatization reactions, as outlined earlier. Consequently, improvements in the efficiency of labeling reactions will ultimately lead to significant improvements in the detection of these analytes by the POCL reaction. A promising trend is to apply this sensitive chemistry in other techniques, e.g., in supercritical fluid chromatography [186] and capillary electrophoresis [56-59], An alter-... 

Supercritical fluid chromatography (SFC) is a relatively recently developed chromatographic technique. Because of its ability to deal with compounds that are either polar or of high molecular weight, much attention has recently focused on applications of SFC to the analysis of different analytes using a variety of fluids or fluid mixtures to provide differing solvent capabilities and select vities. As a result there is a large amount of research currently underway both in SFC method development and in hardware development. 

The first paper on supercritical fluid chromatography (SFC) by Klesper et al. in 1962 [8] considered analytical SCF applications. Only twenty years later, in 1982, a first patent on the use of SFC for production purposes was granted by Perrut [9]. During these years, various academic and industrial laboratories have demonstrated the feasibility and the applicability on a commercial scale of these chromatographic processes. 

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. 

A supercritical fluid is a substance that comes into existence after the so-called critical point has been exceeded, that is, when it simultaneously exhibits the properties of a gas and a liquid, but is actually neither the one nor the other. In 1962, Klesper, Corwin, and Turner were the first researchers to use supercritical fluids for analytical purposes. A supercritical fluid was used in high-pressure fluid chromatography, where it was part of the mobile phase. Extraction with a supercritical fluid was first achieved in 1978, since when the supercritical fluid extraction (SFE) technique has been undergoing active development, finding many applications in laboratory analysis and industry.212... 

There is a synergism between adsorption and chromatographic processes which is clearly demonstrated in the supercritical fluid literature. Research in supercritical fluid chromatography can usually be divided into analytical applications and the measurement of physicochemical data. Early analytical separations methodology performed at pressures close to ambient conditions... 

The coated polysaccharide-based phases have mostly been used in normal phase conditions, but an increasing number of preparative applications have been reported in supercritical fluid chromatography [33] or reversed phase mode [34]. The broad applicability of the coated polysaccharide-based CSPs has made them very popular and they are now widely used for preparative separation of enantiomers and large-scale applications up to tonnes per year have been reported [35, 36]. The success of these CSPs is documented in numerous papers and these CSPs are the most used phases for analytical and preparative applications. 

Supercritical fluid chromatography (SFC)ls Uses HPLC packed columns and a mobile phase of pressurized supercritical fluids (i.e., carbon dioxide modified with a polar organic solvent). Useful for nonpolar analytes and preparative applications where purified materials can be recovered easily by evaporating the carbon dioxide. HPLC pumps and GC-type detectors are often used. 

Supercritical fluid chromatography (SFC) is not restricted by the volatility or thermal lability of the analyte, which is an advantage compared with GC. Much of the literamre on SFC concerns the analysis of relatively nonpolar materials. However, applications of polar analytes are becoming increasingly prevalent with modified fluids. SFC of organic sulfur compounds has been limited to sulfonamides" " and PASH." ... 

Infrared spectroscopy is probably the most widespread analytical spectroscopic technique for identification and characterization of organic compounds. Because of this identification capability infrared spectroscopy is desirable as a detection technique for chromatographic separations. With the advent of Fourier transform infrared spectroscopy/ the speed and sensitivity of infrared detection is greatly enhanced making such applications feasible. FT-IR detection has been widely accepted as a detector for gas chromatography (GC/FT-IR) (1) and has been applied with limited success to liquid chromatography (LC/FT-IR) (2)/ and more recently to supercritical fluid chromatography (SFC/FT-IR) (3). The recent review articles cited here provide excellent introduction and references to current state-of-the-art in these areas. 

---