Supercritical fluid extraction of analytes

The supercritical fluid extraction of analytes from solid sorbents is controlled by a variety of factors including the affinity of the analytes for the sorbent, the tortuosity of the sorbent bed, the vapor pressure of the analytes, and the solubility and the diffusion coefficient of the analytes in the supercritical fluid. Additionally, SFE efficiencies are affected by a complex relationship between many experimental variables, several of which are listed in Table I. Although it is well established that, to a first approximation, the solvent power of a supercritical fluid is related to its density, little is known about the relative effects of many of the other controllable variables for analytical-scale SFE. A better understanding of the relative effects of controllable SFE variables will more readily allow SFE extractions to be optimized for maximum selectivity as well as maximum overall recoveries. 

Hawthorne, S.B. Miller, D.J. Burford, M.D. Langenfeld, J.J. Eckert-Tilotta, S. Louie, P.K. Factors controlling quantitative supercritical fluid extraction of analytical samples. J. Chromatogr., A 1993, 642 (1-2), 301-317. 

Modey, W.K., Mulholland, D.A., and Raynor, M.W., Analytical supercritical fluid extraction of natural products, Phytochem. Anal, 7, 1, 1996. 

Before the extraction procedure may commence, the sample must be prepared in such a way that it is in a condition for extraction of the analyte(s). For analyzing sulfonamide residues in liquid samples such as milk, a pretreatment dilution step with water prior to direct fluorometric detection may be required (207). Dilution of milk with aqueous buffer (208) or sodium chloride solution (209) prior to sample cleanup has also been reported. For the analysis of honey a simple dissolution of the sample in water (210, 211) or aqueous buffer (212) is generally required. Semisolid samples such as muscle, kidney, and liver, require, however, more intensive sample pretreatment. The analyte(s) must be exposed to extracting solvents to ensure maximum extraction. The most popular approach for tissue break-up is through use of a mincing and/or homogenizing apparatus. Lyophilization (freeze-drying) of swine kidney has been carried out prior to supercritical-fluid extraction of trimethoprim residues (213). 

Supercritical Fluid Extraction of Polar Analytes Using Modified C02 and In Situ Chemical... 

Chesler, S. "The Round Robin Test Materials and a Summary of the Results," Consortium on Automated Analytical Laboratory Systems, 2nd CAALS Workshop on Supercritical Fluid Extraction of Solid Environmental Samples, November 8, 1991, NIST, Gaithersburg, MD. 

U. Ullsten and K. E. Markides, Automated on-line solid phase adsorption/supercritical fluid extraction/supercritical fluid chromatography of analytes from polar solvents , J. Micmcolumn Sep. 6 385-393 (1994). 

Figure 15.13 Comprehensive two-dimensional GC chromatogram of a supercritical fluid extract of spiked human serum. Peak identification is as follows 1, dicamba 2, trifluralin 3, dichloran 4, phorate 5, pentachlorophenol 6, atrazine 7, fonofos 8, diazinon 9, chlorothalonil 10, terbufos 11, alachlor 12, matalaxyl 13, malathion 14, metalochlor 15, DCPA 16, captan 17, folpet 18, heptadecanoic acid. Adapted from Analytical Chemistry, 66, Z. Liu et al., Comprehensive two-dimensional gas chromatography for the fast separation and determination of pesticides extracted from human serum , pp. 3086-3092, copyright 1994, with permission from the American Chemical Society.

Meyer et al. [173] showed that supercritical fluid extraction results can give recoveries comparable to Soxhlet extraction methods, even for soils with high carbon contents. McNally et al. [174] have studied factors affecting the supercritical fluid extraction of soils. It was shown that soil type affects the recovery of moderately polar analytes. In general the organic carbon content of the soil governs analytical recovery. 

Papilloud, S. and W. Haerdi (1995). Supercritical fluid extraction of triazine herbicides A powerful selective analytical method. 

Fahmy, T.M., Pulaitis, M.E., Johnson, D.M., McNally, M.E.P., Modifier effects in the supercritical fluid extraction of solutes from clay, soil, and plant materials. Anal. Chem., 65 (10), 1462-1469,1993. Langenfeld, J.J., Hawthorne, S.B., Miller, D.J., Pawliszyn, J., Role of modifiers for analytical scale supercritical fluid extraction of environmental samples. Anal. Chem., 66(6), 909-916,1994. Hawthorne, S.B., Methodology for off-line supercritical fluid extraction. In Supercritical Fluid Extraction and Its Use in Chromatographic Sample Preparation, Westwood S.A. (Ed.), Blackie Academic and Professional, 39-64, 1993. 

The effect of the presence of a modifier, which is critical in the supercritical fluid extraction of PAHs, has been thoroughly studied and compared with that on Soxhlet extraction. The modifier effectively displaces the analytes from the active sites in the matrix, thereby dramatically shortening the extraction time. A series of binary modifiers... 

Recently, the supercritical fluid extraction of PAHs was used to correlate the contents thus obtained with the bioremediation behaviour of the target analytes in a field treatment plot for 1 year based on the results, mild SFE was deemed an expeditious, useful tool for predicting the bioavailability of PAHs in polluted soil [189]. 

J. Damian, L. Myer, P. Liesdheski and J. Tehrani, Supercritical fluid extraction of organic analytes from aqueous media and wet matrices, Pittcon 92, New Orleans (1992). 

J. J. Langenfeld, S. B. Hawthorne, D. J. Miller, J. Pawliszyn, Role of modifiers for analytical-scale supercritical fluid extraction of environmental samples. Anal. Chem., 66 (1994), 909-916. 

Tena, M.T., Valcarel, M., Hidalgo, PJ. and Ubera, J.L. 1997. Supercritical fluid extraction of natural antioxidants from rosemary comparison with liquid solvent sonication. Analytical Chem. 69 521-526. 

Scalia S, Giuffreda L, Pallado P. Analytical and preparative supercritical fluid extraction of chamomile flowers and its comparison with conventional methods. J Pharm Biomed Anal 1998 21 549-558. 

Ma X, Yu X, Zheng Z, Mao J. Analytical supercritical fluid extraction of Chinese herbal medicines. Chromatographia 1991 32 40 4. 

Messer DC, Taylor LT. Development of analytical SFE [supercritical fluid extraction] of a polar drug from an animal food matrix. J High Resolut Chromatogr 1992 15 238-241. 

Moore WN, Taylor LT. Analytical inverse supercritical-fluid extraction of polar pharmaceutical compounds from cream and ointment matrices. J Pharm Biomed Anal 1994 12 1227-1232. 

Hawthorne, S.B., D.J. Miller, D.E. Nivens, and D.C. White. 1992. Supercritical fluid extraction of polar analytes using in situ chemical derivatization. Anal. Chem. 64 405-412. 

Jimenez-Carmona, M. M. and Luque de Castro, M. D., Reverse-micelle formation a strategy for enhancing C02-supercritical fluid extraction of polar analytes. Anal. Chim. Acta, 358, 1-4, 1998. 

Ashraf-Khorassani, M Combs, M.T. Taylor, L.T. Supercritical Fluid Extraction of Inorganics in Environmental Analysis Encylopedia of Analytical Chemistry. John Wiley Sons, 2000 Vol. 4,3410-3423. 

Finally, in recent years the continuing revolutions in instrument hardware have had a profound influence on some areas of lipid analysis. The development of supercritical fluid extraction of lipids now provides an alternative to wet solvent extractions, which have basically remained unchanged in principle and practice since the 1960s. Advances in mass spectrometry and analytical chromatography now allow the direct analysis and identification of complex lipids from total lipid extracts without the requirement for solvent fractionation. 

Kureckova, K., Maralikova, B., and Ventura, K., Supercritical fluid extraction of steroids from biological samples and first experience with solid-phase microextraction-liquid chromatography, Journal of Chromatography B—Analytical Technologies in the Biomedical and Life Sciences, 770, 83-89, 2002. 

CM Wai. Supercritical fluid extraction of trace metals from solid and liquid materials for analytical apphcations. Anal Sci 11 165-167, 1995. 

The main condition to use PS-SFC for a separation is the possibility to dissolve the sample in the supercritical fluid. This solubility can be evaluated from experiments or from literature on the applications of the supercritical fluids (extraction or analytical chromatography) (eg, [9,10]). 

Removing an analyte from a matrix using supercritical fluid extraction (SEE) requires knowledge about the solubiUty of the solute, the rate of transfer of the solute from the soHd to the solvent phase, and interaction of the solvent phase with the matrix (36). These factors collectively control the effectiveness of the SEE process, if not of the extraction process in general. The range of samples for which SEE has been appHed continues to broaden. Apphcations have been in the environment, food, and polymers (37). 

Analytical Supercritical Fluid Extraction and Chromatography Supercritical fluids, especially CO9, are used widely to extrac t a wide variety of solid and hquid matrices to obtain samples for analysis. Benefits compared with conventional Soxhlet extraction include minimization of solvent waste, faster extraction, tunabihty of solvent strength, and simple solvent removal with minimal solvent contamination in the sample. Compared with high-performance liquid chromatography, the number of theoretical stages is higher in... 

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... 

Supercritical fluid extraction (SFE) has been extensively used for the extraction of volatile components such as essential oils, flavours and aromas from plant materials on an industrial as well as an analytical scale (61). The extract thus obtained is usually analysed by GC. Off-line SFE-GC is frequently employed, but on-line SEE-GC has also been used. The direct coupling of SEE with supercritical fluid chromatography (SEC) has also been successfully caried out. Coupling SEE with SEC provides several advantages for the separation and detection of organic substances low temperatures can be used for both SEE and SEC, so they are well suited for the analysis of natural materials that contain compounds which are temperature-sensitive, such as flavours and fragrances. 

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. 

Although on-line sample preparation cannot be regarded as being traditional multidimensional chromatography, the principles of the latter have been employed in the development of many on-line sample preparation techniques, including supercritical fluid extraction (SFE)-GC, SPME, thermal desorption and other on-line extraction methods. As with multidimensional chromatography, the principle is to obtain a portion of the required selectivity by using an additional separation device prior to the main analytical column. 

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