On-line supercritical fluid extraction

B. Mumgaverl and K. J. Voorhees, On-line supercritical fluid extraction/chromatography system for trace analysis of pesticides in soybean oil and rendered fats , ]. Microcolumn Sep. 3 11-16(1991). 

Pressurized Fluid Extraction followed by Gas Chromatography/Mass Spectrometry (PFE-GC/MS) On-line Supercritical Fluid Extraction - Gas Chromatography/Mass Spectrometry (SFE-GC/MS)... 

On-line supercritical fluid extraction/GC methods combine the ability of liquid solvent extraction to extract efficiently a broad range of analytes with the ability of gas-phase extraction methods to rapidly and efficiently transfer the extracted analytes to the gas chromatograph. The characteristics of supercritical fluids make them ideal for the development of on-line sample extraction/gas chromatographic (SFE-GQ techniques. SFE has the ability to extract many analytes from a variety of matrices with recoveries that rival liquid solvent extraction, but with much shorter extraction times. Additionally, since most supercritical fluids are converted to the gas phase upon depressurization to ambient conditions, SFE has the potential to introduce extracted analytes to the GC in the gas phase. As shown in Fig. 13.8, the required instrumentation to perform direct coupling SFE-GC includes suitable transfer lines and a conventional gas chromatograph [162,163]. 

Hawthorne, S. B. Coupled (on-line) supercritical fluid extraction-gas chromatography. In Supercritical Fluid Extraction and Its Use in Chromatographic Sample Preparation, Westwood, S. A. Ed., Blackie Academic and Professional, Chapman and Hall UK, 1993 p. 65. 

Raymer JH, Velez GR. 1991. Development of a flexible, on-line supercritical fluid extraction-gas chromatographic (SFE-GC) system. J Chromatogr Sci 29 467-475. 

Another powerful means of sample introduction is direct, on-line supercritical fluid extraction. A small amount of solid (or liquid) sample can be placed in an extraction vessel, followed by the introduction of the supercritical fluid. The material can be... 

C. Mougin and J. Dubroca, On-line supercritical fluid extraction and high performance liquid chromatography for determination of triazine compounds in soil, J. High Resolut. Chromatogr 19 700-702 (1996). 

In general, supercritical fluid extractions can be performed in either an on-line extraction mode or an off-line extraction mode. Off-line supercritical fluid extraction is the most common mode and involves extracting the analytes from the matrix and collecting them in either a sorbent trap or a collection solvent [11]. Following the collection step, the analytes are determined on a separate instrument (for example, on a chromatograph or an infrared spectrometer). In the on-line supercritical fluid extraction experiment, the outlet of the supercritical fluid extraction system is connected to a second analytical... 

Oudsema, J.W. and Poole, C.F. (1992) On-line supercritical fluid extraction and chromatography of organotins with packed microbore columns and formic acid modified carbon dioxide. Fresenius J. Anal. Chem., 344, 426-434. 

Shimmo, M., A. Piia, K. Hartonem, et al. 2004. Identification of organic compounds in atmospheric aerosol particles by on-line supercritical fluid extraction-liquid chromatography-gas chromatography-mass spectrometry./. Chromatogr. A 1022 151-159. 

To gain further information concerning the hexane fractions, on-line supercritical fluid extraction/SFC was coupled with on-line FTIR detection. FT1R should have an advantage in that it is more sensitive to aliphatic hydrocarbons than the UV detector. 

M. Lohleit, K. Bachmann, Integrated analysis of solid samples by on-line supercritical fluid extraction-gas chromatography, J. Chromatogr., 505 (1990), p. 227. 

Turner C, King JW, Mathiasson L. On-line supercritical fluid extraction/en-zymic hydrolysis of vitamin A esters a new simplified approach for the determination of vitamins A and E in food. J Agric Food Chem 2001 49 553-558. 

Alley EG, Lu G. 1995. Analysis of polychlorinated biphenyls in fatty biological matrixes by on-line supercritical fluid extraction and supercritical fluid cleanup. J AOAC Int 78(4) 1051-1054. 

Off-line supercritical fluid extraction, ultrasonic supercritical fluid extraction, and on-line supercritical fluid extraction-gas chromatography methodologies that have been developed specifically for analytical sample preparation and analysis are described. These methods offer the potential for extraction rate increases of over an order of magnitude, and are compatible with online analysis which provides the basis for automated sample preparation and analysis. These methods are particularly useful for small sample sizes or trace levels of analytes, and have been demonstrated to operate quantitatively. Combined ultrasonic supercritical fluid extraction can further enhance extraction rates from macro-porous materials by inducing convection through internal pores. The apparatus and instrumentation are described in detail and several examples are presented illustrating the applicability of these methodologies. 

Figure 6. Schematic diagram of the on-line supercritical fluid extraction-gas chromatography instrumentation. (Reproduced from Ref. 13. Copyright 1987 American Chemical Society.)...

Off-line supercritical fluid extraction, simultaneous ultrasonic supercritical fluid extraction, and on-line supercritical fluid extraction-gas chromatography have been described. These analytical supercritical fluid extraction methods provide the potential for very rapid extraction rates and compatibility with on-line analytical methods. Extraction rate increases of over an order of magnitude compared to Soxhlet methods have been demonstrated and even greater increases seem feasible. Optimization of fluid solvating conditions also provides the potential for selective fractionation of specific analytes. The application of ultrasound during supercritical fluid extraction provides an efficient... 

By changing the density of the snpercritical flnid, different fractions may be selectively extracted from the complex mixtnre or simple matrix. On decompression, the extracted solntes are precipitated and may be collected from injection into a gas chromatography or SFC for analysis. Figure 7.2 shows a simple apparatus for on-line supercritical fluid extraction (SFE)/SFC solutes extracted from the sample matrix are deposited from the end of a restrictor into the internal loop of the microinjection valve of the capillary SFC. The valve loop contents are subsequently switched into the SFC column by means of liquid or supercritical carbon dioxide. 

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