Supercritical fluid extraction apparatus

Figure 15.4 shows a schematic diagram of a supercritical fluid extraction apparatus. The advantages of supercritical fluid extraction (SFE) are as follows ... 

Figure 1. Schematic representation of supercritical fluid extraction apparatus.

Since commercial supercritical fluid extraction apparatus has become available, use of these materials as extractants has become attractive. Solvent evaporation and disposal are eliminated, and the extractions may be very efficient because of the low viscosity of supercritical fluids, which allows them to penetrate readily into the solid sample particles. Carbon dioxide, with or without modifiers such as methanol, is the most commonly used solvent. 

Figure 1. Schematic diagram of the off-line supercritical fluid extraction apparatus. (Reproduced from Ref. 12. Copyright 1987 American Chemical Society.)...

Figure 9. Schematic of a supercritical fluid extraction apparatus with clathrate vessel (Reproduced with permission from Ref. 18. Copyright 1986 Gakkai Shuppan Senta.)...

SFC-TLC is largely unexplored. Stahl [927] developed a device for supercritical fluid extraction with deposition of the fluid extracts on a moving TLC plate. Wunsche et al. [928] have described an automated apparatus for direct pSFC-TLC coupling. Compared to collecting the effluent from the SFC in decompression vessels, the direct deposition of the effluent on the TLC plate leads to significant losses of analytes. Multidimensional SFC has been reviewed [929]. 

The main comparisons between extraction methods have been made between the Soxhlet, ultrasonication, and supercritical fluid extraction [377, 398,456,461,462]. This has primarily been prompted by the need to evaluate critically the relative merits of SFE as an alternative to the more established methods. Richards and Campbell [456] made a comparison between SFE, Soxhlet, and sonication methods for the determination of some priority pollutants in soil. The SFE apparatus was the same, relatively standard system as described by Campbell et al. [457] with the addition of a C02 cryogenic trap to... 

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). 

Extraction In order to extract the toxin from the matrix, solvents or mixtures of solvents (methylene chloride, bicarbonate solution, methanol-water, chloroform-water) are used. Two main types of apparatus are commonly used the mechanical shaker (Ultra-Turrax homogenizer, multi-Wrist, magnetic stirrer) or High-Speed Waring Blenders. Other, rarely used extraction procedures are Soxhlet-type extractors and, more recently, supercritical fluid extraction. The time of extraction ranges from a few minutes (3 - 5) to 1 hour, depending on the procedure employed. 

The adaptation of supercritical fluid extraction (SFE) in routine residue and metabolism analysis as well as other extraction/separation laboratories and applications has been slow. This is despite the demonstrated feasibility of using SFE for the removal of sulfonylureas, phenylmethylureas and their metabolites from soil and plant materials (1-2), as well as widespread demonstrated use of supercritical fluid extraction for other applications (3-6). The reason for this is simple. Although automated, SFE extraction apparatus typically only analyzes a single sample at a time. The technique could not compete effectively with the productivity of an experienced technician performing many sample extractions simultaneously. In essence, with a one vessel automated supercritical fluid extractor, operator attendance is high and throughput is about the same or even less than current conventional liquid-liquid and solid-liquid extraction techniques. 

A novel combination of two non-polluting engineering steps has been demonstrated mediated electrooxidation (MEO) and supercritical fluid extraction (SFE). The combination has an application potential for waste destruction and organic synthesis. A small apparatus has been constructed for each application. 

Figure 7. Laboratory Apparatus for Supercritical Fluid Extraction.

Alternatively, one could use a Soxhlet or similar apparatus to extract the sample. Other methods to prepare a sample for analysis through extraction include supercritical fluid extraction (SFE), pressurized fluid extraction, and microwave-assisted solvent extraction. 

In the experiments of O Connor et al., monodisperse PFPE Z and Zdol, which were fractionated via supercritical fluid extraction in CO2, were dip-coated onto the surface of silicon wafers as shown in Fig. 2A. Film thickness was controlled by altering the PFPE concentration and draw rate. An SME apparatus (Fig. 2B)... 

Many variations and special apparatus have been developed over the decades to solve specific problems and to do extractions more efficiently. Several of these are solvent heavier than water (Chapter 10) solvent lighter than water (Chapter 10) continuous countercurrent (Chapter 11) solid phase extraction (Chapter 12) liquid-solid extraction, microwave heated solvents (Chapter 10) and supercritical fluid extraction (Chapter 13). 

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. 

Some techniques that combine the properties of extraction and cleanup are supercritical fluid extraction (SEE) and matrix solid-phase dispersion (MSPD). Supercritical fluids, i.e., at a temperature and pressure in excess of their critical point, have unique properties for selective extraction of analytes from a sample. Solid samples are mixed with an inert dispersant, such as hydromatrix, and the mixture packed into the cell of the SEE apparatus. The sample is extracted with supercritical CO2, with or without addition of organic modifier, and the extracted analytes may be collected inline or offline on suitable adsorbents (Figure 3). Further cleanup of the sample extract may be performed using SPE. MSPD is based on intimate mixing of animal tissue sample with a bonded silica, such as Cig, and packing of the blended material into a column from which interferences can be eluted by washing with solvents and the analytes eluted using a selective solvent. 

Sato. M. Goto. M. Hirose, T. (1996) Supercritical fluid extraction for the removal of terpenes from citnis oils, Proc. of the International Solvent Extraction Conference, Melbourne, Australia, vol. 2, 987. Meyer, J. -T., Brunner. G. (1994) Apparatus for determination of hydrodynamic behavior in countercurrent columns and some experimental results. Proceedings 3rd International Svmpo.sium on Supercritical Fluids. Pemit M., Brunner, G. (eds.), Strasbourg, ISBN 2-905267-23-8. Vol. 2, 217 - 222. 

Figure 8.4 Apparatus for coupled supercritical fluid extraction/SFC...

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