Supercritical fluid chromatograph extraction

Studies designed to improve the determination of environmental contaminants will continue to provide refinements and improvements in the determination of acrylonitrile. The current high level of activity in supercritical fluid extraction of solid and semisolid samples should yield improved recoveries and sensitivities for the determination of acrylonitrile in solid wastes, and the compound should be amenable to supercritical fluid chromatographic analysis. Immunoassay analysis is another area of intense current activity from which substantial advances in the determination of acrylonitrile in environmental samples can be anticipated (Vanderlaan et al. 1988). 

The supercritical fluid chromatographic procedure [20] described in section 9.1.1.5 for the determination of organochlorine insecticides in soils has also been applied to river sediments. Snyder et al. [20] compared supercritical fluid extraction with classical sonication and Soxhlet extraction for selected organochlorine insecticides. Samples of sediments extracted with supercritical carbon dioxide modified with 3% methanol at 350atm and 50°C gave =85% recovery of organochlorine insecticides including Dichlorvos, Diazinon, Endrin, Endrin aldehyde, decachlorobiphenyl, p,p -DDT and Mirex. 

Following their extraction and cleanup, residues of sulfonamides and diaminopyrimidine potentiators in sample extracts can be detected by direct nonchro-matographic methods, or thin-layer, gas, liquid, or supercritical fluid chromatographic methods (Table 29.7). 

The relative effects of supercitical carbon dioxide density, temperature, extraction cell dimensions (I.D. Length), and cell dead volume on the supercritical fluid extraction (SFE) recoveries of polycyclic aromatic hydrocarbons and methoxychlor from octadecyl sorbents are quantitatively compared. Recoveries correlate directly with the fluid density at constant temperature whereas, the logarithms of the recoveries correlate with the inverse of the extraction temperature at constant density. Decreasing the extraction vessels internal diameter to length ratio and the incorporation of dead volume in the extraction vessel also resulted in increases in SFE recoveries for the system studied. Gas and supercritical fluid chromatographic data proved to be useful predictors of achievable SFE recoveries, but correlations are dependent on SFE experimental variables, including the cell dimensions and dead volume. 

For the on-line SFE-NMR experiments, the set-up shown in Figure 7.2.17 can be used. A main pump serves an HP supercritical fluid chromatograph (G1205A), with analytical HPLC columns being used as extraction cells. The continuous-flow NMR cell is connected between the column outlet and the back-pressure regulator. 

The development of supercritical fluid (SCF) extraction combined with chromatographic analysis will probably be useful for meeting the goals of quantitative, rapid, easily performed, low cost and safe procedures for the determination of poorly volatile organic analytes such as nitrobenzene and its metabolites in biological samples (Hawthorne 1988). 

Also supercritical fluid chromatograph (SFC) has been combined with SFE 13,42). For example, SFE-SFC has been developed for the characterization of compounds in desert botanical species Dalea spinosa) (13). A slightly more complex combination utilizing SFE-SFC-GC has been developed for the determination of volatile compounds in raw and baked Baltic herring Clupea harengus membras) 14). In this study, the analytes were extracted with supercritical CO2 (45 C, 10 MPa) and the volatiles and coeluted lipids were separated on-line using SFC, and the volatile fraction was introduced directly into a GC. 

Bartle, K.D., Clifford, A. A., Fang, R., Jafar, S. A., Symposium on Extraction and Chromatography with Supercritical Fluids, Chromatographic Society and University of Keele, Keele, 2-3 October 1991. 

The development of methods of analysis of tria2ines and thek hydroxy metabohtes in humic soil samples with combined chromatographic and ms techniques has been described (78). A two-way approach was used for separating interfering humic substances and for performing stmctural elucidation of the herbicide traces. Humic samples were extracted by supercritical fluid extraction and analy2ed by both hplc/particle beam ms and a new ms/ms method. The new ms /ms unit was of the tandem sector field-time-of-flight/ms type. 

Numerous high pressure Hquid chromatographic techniques have been reported for specific sample forms vegetable oHs (55,56), animal feeds (57,58), seta (59,60), plasma (61,62), foods (63,64), and tissues (63). Some of the methods requite a saponification step to remove fats, to release tocopherols from ceHs, and/or to free tocopherols from their esters. AH requite an extraction step to remove the tocopherols from the sample matrix. The methods include both normal and reverse-phase hplc with either uv absorbance or fluorescence detection. AppHcation of supercritical fluid (qv) chromatography has been reported for analysis of tocopherols in marine oHs (65). 

Supercritical fluid extraction (SFE) and Solid Phase Extraction (SPE) are excellent alternatives to traditional extraction methods, with both being used independently for clean-up and/or analyte concentration prior to chromatographic analysis. While SFE has been demonstrated to be an excellent method for extracting organic compounds from solid matrices such as soil and food (36, 37), SPE has been mainly used for diluted liquid samples such as water, biological fluids and samples obtained after-liquid-liquid extraction on solid matrices (38, 39). The coupling of these two techniques (SPE-SFE) turns out to be an interesting method for the quantitative transfer... 

S. A. Westwood (Ed.), Supercritical Fluid Extraction and its Use in Chromatographic Sample Preparation, CRC Press, Boca Raton, PE (1992). 

In order to reduce or eliminate off-line sample preparation, multidimensional chromatographic techniques have been employed in these difficult analyses. LC-GC has been employed in numerous applications that involve the analysis of poisonous compounds or metabolites from biological matrices such as fats and tissues, while GC-GC has been employed for complex samples, such as arson propellants and for samples in which special selectivity, such as chiral recognition, is required. Other techniques include on-line sample preparation methods, such as supercritical fluid extraction (SFE)-GC and LC-GC-GC. In many of these applications, the chromatographic method is coupled to mass spectrometry or another spectrometiic detector for final confirmation of the analyte identity, as required by many courts of law. 

The coupling of supercritical fluid extraction (SEE) with gas chromatography (SEE-GC) provides an excellent example of the application of multidimensional chromatography principles to a sample preparation method. In SEE, the analytical matrix is packed into an extraction vessel and a supercritical fluid, usually carbon dioxide, is passed through it. The analyte matrix may be viewed as the stationary phase, while the supercritical fluid can be viewed as the mobile phase. In order to obtain an effective extraction, the solubility of the analyte in the supercritical fluid mobile phase must be considered, along with its affinity to the matrix stationary phase. The effluent from the extraction is then collected and transferred to a gas chromatograph. In his comprehensive text, Taylor provides an excellent description of the principles and applications of SEE (44), while Pawliszyn presents a description of the supercritical fluid as the mobile phase in his development of a kinetic model for the extraction process (45). 

Current interest in supercritical fluid extraction as a sample preparation technique for chromatographic analysis is intense, in spite of it receiving very little tion until the mid-1980s. Although neglected by analytical cl Hsts, during the... 

Figure 3.10 Optimisation strategy for supercritical fluid extraction of polymeric samples. After Lou et al. [145]. Reproduced from the Journal of Chromatographic Science by permission of Preston Publications, A Division of Preston Industries, Inc.

A.L. Howard and L.T. Taylor, in Supercritical Fluid Extraction and Its Use in Chromatographic Sample Preparation (S.A. Westwood, ed.), Blackie, London... 

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