Supercritical fluid extraction modifiers

One example of normal-phase liquid chromatography coupled to gas chromatography is the determination of alkylated, oxygenated and nitrated polycyclic aromatic compounds (PACs) in urban air particulate extracts (97). Since such extracts are very complex, LC-GC is the best possible separation technique. A quartz microfibre filter retains the particulate material and supercritical fluid extraction (SPE) with CO2 and a toluene modifier extracts the organic components from the dust particles. The final extract is then dissolved in -hexane and analysed by NPLC. The transfer at 100 p.1 min of different fractions to the GC system by an on-column interface enabled many PACs to be detected by an ion-trap detector. A flame ionization detector (PID) and a 350 p.1 loop interface was used to quantify the identified compounds. The experimental conditions employed are shown in Table 13.2. 

Supercritical fluid extraction — During the past two decades, important progress was registered in the extraction of bioactive phytochemicals from plant or food matrices. Most of the work in this area focused on non-polar compounds (terpenoid flavors, hydrocarbons, carotenes) where a supercritical (SFE) method with CO2 offered high extraction efficiencies. Co-solvent systems combining CO2 with one or more modifiers extended the utility of the SFE-CO2 system to polar and even ionic compounds, e.g., supercritical water to extract polar compounds. This last technique claims the additional advantage of combining extraction and destruction of contaminants via the supercritical water oxidation process."... 

Supercritical fluid extraction (SFE) is a technique in which a supercritical fluid [formed when the critical temperature Tf) and critical pressure Pf) for the fluid are exceeded simultaneously] is used as an extraction solvent instead of an organic solvent. By far the most common choice of a supercritical fluid is carbon dioxide (CO2) because CO2 has a low critical temperature (re = 31.1 °C), is inexpensive, and is safe." SFE has the advantage of lower viscosity and improved diffusion coefficients relative to traditional organic solvents. Also, if supercritical CO2 is used as the extraction solvent, the solvent (CO2) can easily be removed by bringing the extract to atmospheric pressure. Supercritical CO2 itself is a very nonpolar solvent that may not have broad applicability as an extraction solvent. To overcome this problem, modifiers such as methanol can be used to increase the polarity of the SFE extraction solvent. Another problem associated with SFE using CO2 is the co-extraction of lipids and other nonpolar interferents. To overcome this problem, a combination of SFE with SPE can be used. Stolker et al." provided a review of several SFE/SPE methods described in the literature. 

Supercritical fluid extraction (SFE) is generally used for the extraction of selected analytes from solid sample matrices, but applications have been reported for aqueous samples. In one study, recoveries of 87-100% were obtained for simazine, propazine, and trietazine at the 0.05 ug mL concentration level using methanol-modified CO2 (10%, v/v) to extract the analytes, previously preconcentrated on a C-18 Empore extraction disk. The analysis was performed using LC/UV detection. Freeze-dried water samples were subjected to SFE for atrazine and simazine, and the optimum recoveries were obtained using the mildest conditions studied (50 °C, 20 MPa, and 30 mL of CO2). In some cases when using LEE and LC analysis, co-extracted humic substances created interference for the more polar metabolites when compared with SFE for the preparation of the same water sample. ... 

Fernandez et al. [9] used supercritical fluid extraction combined with ion pair liquid chromatography to determine quaternary ammonium in digested sludges and marine sediments. Carbon dioxide modified with 30% methanol was used as the extractant at an operating pressure of 380atm. Between 0.2 and 3.7g kg-1 surfactant was found in Swiss works effluent sludges, determined with a relative standard deviation of 7%. 

Snyder et al. [20] have compared supercritical fluid extraction with classical sonication and Soxhlet extraction for the extraction of selected pesticides from soils. Samples extracted with supercritical carbon dioxide modified with 3% methanol at 350atm and 50°C gave a =85% recovery of organochlorine insecticides including Dichlorvos, Endrin, Endrin aldehyde, p,p -DDT mirex and decachlorobiphenyl (and organophosphorus insecticides). 

Snyder et al. [94] compared supercritical extraction with classical sonication and Soxhlet extraction for the extraction of selected organophosphorus insecticides from soil. Samples extracted with supercritical carbon dioxide modified with 3% methanol at 350atm and 50°C gave a =85% recovery of Diazinon (diethyl-2-isopropyl-6-methyl-4-pyrimidinyl phosphorothiodate or 0,0 diethyl-0-(2-isopropyl-6-methyl-4-pyrimidyl) phosphorothioate). Ronnel (or Fenchlorphos) 0,0-dimethyl-0-2,4,5 trichlorophenol phosphorothiodate), Parathion ethyl (diethyl-p-nitrophenyl (phosphorothioate), Tetrachlorovinphos (trans,-2-chloro-l-(2,4,5 trichlorophenyl) vinyl (chlorophenyl-O-methylphenyl phosphorothioate) and Methiadathion. Supercritical fluid extraction with methanol modified carbon dioxide has been applied to the determination of organophosphorus insecticides in soil [260]. 

Supercritical fluid extraction with methanol modified carbon dioxide has been applied to the determination of Triazine herbicides in soil [103]. 

The method based on immunosorbents coupled on-line with liquid chromatography-atmospheric pressure chemical ionization mass spectrometry [109], discussed in section 9.4.2.1, has been applied to the determination of substituted urea type herbicides. Supercritical fluid extraction with methanol modified carbon dioxide has been applied to the determinants of sulfonyl urea herbicides in soil [261],... 

Fahing et al. [24] studied the modifier effects in the supercritical fluid extraction of organics from soils and clays. Swelling experiments showed that unmodified carbon dioxide did not cause swelling of the soil whereas carbon dioxide modified with water did cause rapid swelling of soil, thereby facilitating extraction of the organics. 

Non-ionic surfactants of a commercial washing powder were separated by supercritical fluid chromatography (SFC) and determined by APCI-MS. The constituents were first extracted by supercritical fluid extraction (SFE) using C02 with or without methanol as a modifier. Variations of the conditions resulted in a selective extraction of the analytes, which could be determined without further purification. Six groups of surfactants were observed, four of which are alkyl-polyethoxylates. The presence of APEO could be excluded by identification recording SFC-FTIR (Fourier transform infrared) spectra [31]. 

Tzeng TC, Lin YL, Jong TT, Chang CMJ. (2007) Ethanol modified supercritical fluids extraction of scopoletin and artemisinin from Artemisia annua L. Separ PurifTech 56 18-24. 

Carotenoids A large number of solvents have been used for extraction of carotenoids from vegetables matrices, such as acetone, tetrahydrofuran, n-hexane, pentane, ethanol, methanol, chloroform [427-431], or solvent mixtures such as dichloromethane/methanol, tetrahydrofuran/methanol, -hexane/acetone, or toluene or ethyl acetate [424,432-435], SPE has been used as an additional purification step by some authors [422,426], Supercritical fluid extraction (SEE) has been widely used, as an alternative method, also adding CO2 modifiers (such as methanol, ethanol, -hexane, water, methylene chloride) to increase extraction efficiency [436-438], In addition, saponification can be carried out, but a loss of the total carotenoid content has been observed and, furthermore, direct solvent extraction has been proved to be a valid alternative [439],... 

As its name suggests, supercritical fluid extraction (SEE) relies on the solubilizing properties of supercritical fluids. The lower viscosities and higher diffusion rates of supercritical fluids, when compared with those of liquids, make them ideal for the extraction of diffusion-controlled matrices, such as plant tissues. Advantages of the method are lower solvent consumption, controllable selectivity, and less thermal or chemical degradation than methods such as Soxhlet extraction. Numerous applications in the extraction of natural products have been reported, with supercritical carbon dioxide being the most widely used extraction solvent. However, to allow for the extraction of polar compounds such as flavonoids, polar solvents (like methanol) have to be added as modifiers. There is consequently a substantial reduction in selectivity. This explains why there are relatively few applications to polyphenols in the literature. Even with pressures of up to 689 bar and 20% modifier (usually methanol) in the extraction fluid, yields of polyphenolic compounds remain low, as shown for marigold Calendula officinalis, Asteraceae) and chamomile Matricaria recutita, Asteraceae). " ... 

The efficacy of supercritical fluid extraction (SFE) for the recovery of 16 common organochlorine pesticides (OCPs) from liquid whole eggs was investigated by employing supercritical carbon dioxide (SC-C02) without the use of a solvent modifier to minimize interfering coextractives (Fiddler et al., 1999). 

In summary, there are four major parameters in SFE that can be modified to obtain good selectivity pressure, temperature, extraction period and choice of modifier. Supercritical fluid extraction is easily automated and can be economically viable if the number of samples is large. 

Supercritical carbon dioxide modified with 10 vol% methanol has been employed for the removal of the amine surfactant in hexagonal mesoporous silica (HMS). The effects of temperature and pressure on the extraction efficiency have been extensively studied. It has been found that within an hour, as high as 96% of the amine surfactant can be extracted at a relatively mild condition of 85°C and 100 bar. At constant pressure, high extraction efficiencies are obtained at 50 and 85°C while at constant temperature, high efficiencies occur at 100 bar and 250 bar. This work establishes the feasibility of using supercritical fluid extraction (SFE) for the removal of the amine surfactant. In fact, it has been discovered that SFE produces EIMS of more enhanced mesoporosity as compared to that of calcination. 

As such, supercritical fluid extraction (SFE) has been proposed for the removal of the amine surfactant. In this work, 1.8 ml/min of CO2 modified with 0.2 ml/min of methanol has been employed for the extraction purpose. Through SFE, recycling of surfactant can be accomplished while generating minimal liquid solvent (methanol) for disposal. Supercritical CO2, which forms the solvent bulk, can be easily separated from the extract (and methanol) via depressurisation and the resultant gas can then either be recycled or be released into the atmosphere. 

Polycyclic aromatic hydrocarbons (PAHs) have been extracted from contaminated land samples by supercritical fluid extraction jSFE) with both pure and modified carbon dioxide. Removing an analyte from a matrix using SFE requires knowledge about die solubility of the solute, the rate of transfer of the solute from the solid to the solvent phase, and interaction of the solvent phase with the matrix. These faclors collectively control the effectiveness of the SFF process, if not of the extraction process in general. The range of samples for which SFE has been applied continues to broaden. Applications have been in the environment, food, and polymers. 

Environmental applications of SFE appear to be the most widespread in the literature. A typical example is the comparison of extraction efficiency for 2,3,7,8 -tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) from sediment samples using supercritical fluid extraction and five individual mobile phases with Soxhlet extraction was made (101). The mobile phases, carbon dioxide, nitrous oxide, pure and modified with 2% methanol as well as sulfur hexafluoride were examined. Pure nitrous oxide, modified carbon dioxide and modified nitrous oxide systems gave the recoveries in the acceptable range of 80 to 100%. Carbon dioxide and sulfur hexafluoride showed recoveries of less than 50% under identical conditions. Classical Soxhlet recoveries by comparison illustrated the poorest precision with average extraction efficiencies of less than 65%. Mobile phase choice, still as yet a major question in the science of supercritical fluid extraction, seems to be dependent upon several factors polarity of the solute of interest, stearic interactions, as well as those between the matrix and the mobile phase. Physical parameters of the solute of interest, as suggested by King, must also be considered. Presently, the science behind the extraction of analytes of interest from complex matrices is not completely understood. 

Supercritical fluid extraction conditions were investigated in terms of mobile phase modifier, pressure, temperature and flow rate to improve extraction efficiency (104). High extraction efficiencies, up to 100%, in short times were reported. Relationships between extraction efficiency in supercritical fluid extraction and chromatographic retention in SFC were proposed. The effects of pressure and temperature as well as the advantages of static versus dynamic extraction were explored for PCB extraction in environmental analysis (105). High resolution GC was coupled with SFE in these experiments. 

We have designed and constructed two instruments that will allow supercritical fluid extraction from plants and soils with modifiers. Other uses, remain to be investigated. These multi-vessel extractors have demonstrated fast and efficient recovery data from a large num-... 

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

In this paper, the supercritical fluid extraction (SFE) of organic compounds from sand spiked with 36 nitroaromatic compounds, 19 haloethers, and 42 organochlorine pesticides, and from a standard reference material certified for 13 polynuclear aromatic hydrocarbons (PAH), dibenzofuran, and pentachlorophenol was examined using a two- and a four-vessel extractor. Although the results achieved by SFE for the sand and the standard reference soil samples were very encouraging, previous data obtained in our laboratory on the standard reference soil and a few other standard reference marine sediments were less favorable. It was therefore decided that an investigation of seven variables for their influence on the analyte recoveries from the standard soil sample would be useful. Two tests were conducted in which these variables were investigated. In Test 1, the seven variables selected were pressure, temperature, moisture content, cell volume, sample size, extraction time, and modifier volume. In Test 2, the seven variables were pressure, temperature, volume of toluene added to the matrix, volume of solvent in the collection vessel,... 

Supercritical fluid extraction (SFE) is a new and promising technique for sample preparation. Because SFE is so new, and there are so many control parameters available to the scientist, it can be difficult to know how to proceed when developing an SFE method. This paper discusses two samples and describes a systematic approach for evaluating SFE extraction parameters for methods development. The effects of modifiers are investigated. 

---