Supercritical fluids, extraction

Supercritical fluid extraction (SFE) utilizes the unique properties of supercritical fluids to facilitate the extraction of organics from solid samples. Analytical scale SFE can be configured to operate on- or off-line. In the online configuration, SFE is coupled directly to an analytical instrument, such as a gas chromatograph, SFC, or high-performance liquid chromatograph. This offers the potential for automation, but the extract is limited to analysis by the dedicated instrument. Off-line SFE, as its name implies, is a stand-alone extraction method independent of the analytical technique to be used. Off-line SFE is more flexible and easier to perform than the online methods. It allows the analyst to focus on the extraction per se, and the extract is available for analysis by different methods. This chapter focuses on off-line SFE. 

Supercritical fluid extraction (SEE) has become a method of choice for the extraction of plant material [14]. It represents an interesting alternative technique compared to conventional liquid-solid extraction, with lower solvent consumption and working temperature. The free bases of hyoscyamine and scopolamine are extractable with 

Cocaine has been extracted from coca leaves and the optimization procedure was investigated by means of a central composite design [17]. Pressure, temperature, nature, and percentage of polar modifier were studied. A rate of 2 mL/min CO2 modified by the addition of 29 % water in methanol at 20 M Pa for 10 min allowed the quantitative extraction of cocaine. The robustness of the method was evaluated by drawing response surfaces. The same compound has also been extracted by SEE from hair samples [18-20]. 

A supercritical fluid extraction is a gas-solid extraction in which the extracting agent is a gas under supercritical conditions. The low viscosity and near zero surface tension permit this gas to penetrate solids far better and quicker than most liquids, and when the extraction is complete, the gas is removed from the extract by simply lowering the pressure. 

Normally, if you want to dissolve a compound, you first select a solvent that has a similar polarity (like dissolves like) then you try to get as much contact (large surface area) as possible between the molecules of solvent and the compound to be dissolved and heat the solvent to further increase the number of collisions. One reason liquids are preferred to gases as solvents is that a high concentration of molecules attacks the surface of the compound to be dissolved, and, therefore, more solvent-solute bonds can be formed to compete with the solute-solute bonds of the solid or liquid. The difficulty with liquid solvents is that once the compound has dissolved, it must now be separated from the solvent. If the compound would dissolve in a gas, then separating the solvent from the solute would be much easier. However, the number of molecules of gas attacking the surface of the compound is quite small compared to that of a liquid, and for that reason, few solids dissolve in gases. What must be done is to make a gas behave like a liquid. If you could compress a gas so it would approach the density of a liquid, then you should get increased solubility and be able to evaporate the gas once the compound was extracted. Under normal conditions, if you compress a gas too much, it may collapse into a liquid. 

What is gained by using supercritical fluids They have gas-like transport properties and their diffusivities are 

After extraction, their high volatility at regular pressures enables them to be separated readily from the solute with little or no residue. This is energy efficient and safety efficient, particularly with foods. 

Notice that most of the critical pressures are below 60 atm or below about 880 p.s.i., pressures which are easily obtainable. Therefore, if you have a pump that can produce several thousand p.s.i., you can alter the pressure to increase the density and the solubility of the material to be extracted should increase. 

Supercritical fluid chromatography (SEC) was developed at an earlier stage (hrst demonstrated in 1962) than SF extraction (SFE), which emerged in the mid-1980s as a promising tool to overcome the difficulties of solid sample extractions.  

Carbon dioxide has been used as a supercritical fluid for the extraction of a variety of phenolic compounds from plant samples. The main advantages of this technique are the use of nontoxic, nonflammable, and inexpensive fluid as CO2, the automation due to the available instruments and the ability of being coupled to chromatographic 

Ultra Performance Liquid Chromatography Mass Spectrometry 

SFE is widely used for the extraction of phenolic compounds from grapes or derivatives [48,67,68] (Table 16.4). Furthermore, this technique has been applied in other matrices such as pepper, tomato, and eggplant by Helmja et al., who compared SFE and UAE. This study indicated that SFE provided the poorest results in ctxnparison with the data obtained by UAE [28]. SFE was also compared with traditional techniques such as Soxhlet extraction using ethyl acetate and ethanol as solvents in guava The best results, in terms of extraction yield (total and fraction) and product quality (antioxidant activity and total phenolic content), were obtained when SFE was tqrplied using ethanol as an organic modifier [66]. The effect of pressure and temperature on the SFE was also evaluated, observing that the most appropriate conditions for the extraction of phenolic compounds was an extraction temperature of 60°C and pressure of 102 bar [66]. 

SFE has also been used in combination with other sample treatment processes, such as nanofiltration approach, for the effective extraction of polyphenols from cocoa seeds [69]. 

A recent development in liquid-liquid extraction has been the use of supercritical fluids as the extraction-solvent. Carbon dioxide at high pressure is the most commonly used fluid. It is used in processes for the decaffeination of coffee and tea. The solvent can be recovered from the extract solution as a gas, by reducing the pressure. Super critical extraction processes are discussed by Humphrey and Keller (1997). 

AIChE (1958) Bubble-tray Design Manual (American Institute of Chemical Engineers). 

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It was observed that the values for virgin LDPE polymers are quantitative in the optimised SEE conditions, as opposed to those for recycled polymers. This was attributed to the higher crystallinity of the recycled LDPE and to sample thickness effects. By reducing the sample thickness to 470 /rm and increasing the dynamic extraction time to 30 min ( SEE drastic conditions ) quantitative results were obtained. Optimum conditions for LDPE/(Irganox 1076, Chimassorb 81) were given as pressure, 450 atm dynamic extraction time, 15 min modifier, 10% (methanol) and extraction temperature, 75 C. 

In the optimised SEE conditions of LDPE none of the additives present in HDPE (Irganox 1076, Irgafos 168) could even be detected. At this point, it may be considered that HDPE shows a more dense molecular stmcture than LDPE. To improve the extraction efficiency, the thickness of the HDPE sample was then reduced to 380 60 fim and the dynamic extraction time was increased to 2 h. Despite 

After Salafranca et al. [44]. From J. Salafranca et al., Journal of High Resolution Chromatography 22, 553-558 (1999). Wiley-VCH, 1999. Reproduced by permission of Wiley-VCH. 

It is also to be noticed that extraction is never complete in finite time in order to obtain the total extractable amount of a compound extrapolation procedures can be used. Clifford [45] has described an extrapolation procedure based on the initial extraction of an amount mi in the period of r = 0-fi, and two subsequent extractions, in equal periods of time terminating at t2 and ty, of amounts m2 and m3. Algebraic manipulation leads to 

Matrix Antioxidant(s) Total extractables (%) Antioxidant concentration (%)  

Numerous applications of SEE were published during the 1980s soon after the availability of commercial instrumentation. Supercritical fluids (SFs) have useful characteristics for the extraction of trace analytes from solid samples, most notably 

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M. A. McHugh and V. J. Knikonis, Supercritical Fluid Extraction, Butterworth Pubhshers, Stoneham, Mass., 1986. 

Supercritical Fluid Extraction. Supercritical fluid (SCF) extraction is a process in which elevated pressure and temperature conditions are used to make a substance exceed a critical point. Once above this critical point, the gas (CO2 is commonly used) exhibits unique solvating properties. The advantages of SCF extraction in foods are that there is no solvent residue in the extracted products, the process can be performed at low temperature, oxygen is excluded, and there is minimal protein degradation (49). One area in which SCF extraction of Hpids from meats maybe appHed is in the production of low fat dried meat ingredients for further processed items. Its apphcation in fresh meat is less successful because the fresh meat contains relatively high levels of moisture (50). 

The concern by consumers about cholesterol has stimulated the development of methods for its removal. Three principal approaches are in the pilot-plant stages use of enzymes, supercritical fluid extraction, and steam distillation. Using known techniques, it is not possible to remove all cholesterol from milk. Therefore, FDA guidelines identify cholesterol-free foods as containing less than 2 mg cholesterol per serving, and low cholesterol foods as containing from 2 to 20 mg (37). 

Purifications of elfamycins have been described in the Hterature using Craig distribution (2,34), chromatography on Sephadex LH-20 (2,14,26) and Amberlite XAD-2 (10,17,19,26), supercritical fluid extraction (37), and chromatography on an Ito multilayer cod planet centrifuge (26,38). and nmr assignments of most elfamycins have been accompHshed (3,24,26,32). The characteristic uv spectra permits some differentiation (12) and bathochromic shifts associated with Al " complexation have been used to quantify efrotomycin (2, R = CH ) in feed premixes (39,40). 

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). 

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. 

Separation Techniques. Current methods for separating fatty acids are by solvent crystaUi2ation or by the hydrophili2ation process. Other methods that have been used in the past, or perhaps could be used in the future, are panning and pressing, solvent extraction, supercritical fluid extraction, the use of metal salts in assisting in separation, separations using urea complexes, and adsorption/desorption. 

FIG. 22-19 Schematic diagram of a typical supercritical fluid-extraction process. 

Adsorption and Desorption Adsorbents may be used to recover solutes from supercritical fluid extracts for example, activated carbon and polymeric sorbents may be used to recover caffeine from CO9. This approach may be used to improve the selectivity of a supercritical fluid extraction process. SCF extraction may be used to regenerate adsorbents such as activated carbon and to remove contaminants from soil. In many cases the chemisorption is sufficiently strong that regeneration with CO9 is limited, even if the pure solute is quite soluble in CO9. In some cases a cosolvent can be added to the SCF to displace the sorbate from the sorbent. Another approach is to use water at elevated or even supercritical temperatures to facilitate desorption. Many of the principles for desorption are also relevant to extraction of substances from other substrates such as natural products and polymers. 

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... 

COMPARISON OF ESSENTIAL OIL COMPOSITION OF SALVIA MIRZAYANII OBTAINED BY SUPERCRITICAL FLUID EXTRACTION AND HYDRODISTILLATION METHODS... 

Supercritical fluid extraction (SFE) has been widely used to the extraction processes in pharmaceutical industries. Besides application of SFE in phannaceuticals, it has been applied on a wide spectmm of natural products and food industries such as natural pesticides, antioxidants, vegetable oil, flavors, perfumes and etc [1-2]. 

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... 

Unfortunately, not much experimental work has been carried out on the combination of Supercritical fluid extraction and liquid chromatography systems (43, 44). One of the reasons for this arises from the difficulties in achieving compatibility between the extraction solvent and the FC mobile phase. Baseline perturbations have been... 

ON-LINE COUPLING OF SUPERCRITICAL FLUID EXTRACTION WITH CAPILLARY ELECTRODRIVEN SEPARATION TECHNIQUES (SFE-CESTs)... 

E. T. Taylor Introduction to Supercritical Fluid Extraction, Research and Development Magazine Publishers, USA (1995). 

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