Methanol-modified extracts

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. ... 

On-line SFE-pSFC-FTD, using formic or acetic acid modified CO2 as an extraction solvent, was used to analyse a dialkyltin mercaptide stabiliser in rigid PVC (Geon 87444) [114]. Hunt et al. [115] reported off-line SFE-pSFC-UV analysis of PVC/(DIOP, chlorinated PE wax, Topanol CA), using methanol as a modifier. Individual additives are unevenly extracted at lower pressures and temperatures, where extraction is incomplete. Topanol CA, the most polar of the three PVC additives studied, could not be fully extracted in the time-scale required (15-20min), even at the highest CO2 temperature and pressure obtainable. However, methanol-modified CO2 enhances extraction of Topanol CA. PVC film additives (DEHP, fatty acids, saturated and aromatic hydrocarbons) were also separated by off-line SFE-preparative SFC, and analysed by PDA and IR [116]. 

On-line SFE-pSFC-FTIR was used to identify extractable components (additives and monomers) from a variety of nylons [392]. SFE-SFC-FID with 100% C02 and methanol-modified scC02 were used to quantitate the amount of residual caprolactam in a PA6/PA6.6 copolymer. Similarly, the more permeable PS showed various additives (Irganox 1076, phosphite AO, stearic acid - ex Zn-stearate - and mineral oil as a melt flow controller) and low-MW linear and cyclic oligomers in relatively mild SCF extraction conditions [392]. Also, antioxidants in PE have been analysed by means of coupling of SFE-SFC with IR detection [121]. Yang [393] has described SFE-SFC-FTIR for the analysis of polar compounds deposited on polymeric matrices, whereas Ikushima et al. [394] monitored the extraction of higher fatty acid esters. Despite the expectations, SFE-SFC-FTIR hyphenation in on-line additive analysis of polymers has not found widespread industrial use. While applications of SFC-FTIR and SFC-MS to the analysis of additives in polymeric matrices are not abundant, these techniques find wide application in the analysis of food and natural product components [395]. 

Barnabas et al. [51] have discussed an experimental design approach for the extraction of polyaromatic hydrocarbons from soil using supercritical carbon dioxide. They studied 16 different polyaromatic hydrocarbons using pure carbon dioxide and methanol modified carbon dioxide. The technique is capable of determining down to lOOmg kgy1 polyaromatic hydrocarbons in soils. 

Hawthorne et al. [53] compared supercritical extraction with chlorodifluoromethane, nitrous oxide and carbon dioxide for the extraction of polychlorobiphenyls and polyaromatic hydrocarbons from soil. Chlorodifluoromethane provided the highest recoveries while methanol modified carbon dioxide gave a 90% recovery of polychlorobiphenyls from soil. 

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],... 

A second SFE-based method for the extraction of NPEC from solid matrices is called subcritical (hot) water extraction [9], The method was applied for NPEi 4C in 0.25 g sludge samples. Subcritical water is used as the extraction solvent, with 30% ethanol as the modifier, yielding quantitative recoveries. Other tested extraction solvent compositions were C02, hot water, methanol-modified hot water, none of which were judged satisfactory. 

A new approach to the analysis of the carcinogenic TSNA in moist snuff tobacco is based on SFE with methanol-modified carbon dioxide. Extracted TSNA are trapped across a glass cartridge filled with Tenax GR, from which they are subsequently released by thermal desorption and analyzed by capillary GC-TEA LOD was <2 ng/g. The technique is fast, reproducible, highly selective and sensitive617. SFE with carbon dioxide was also used in the analysis of TSNA in smokeless tobacco. It revealed the presence of higher levels of 4-(methylnitrosamino)-l-(3-pyridyl)-l-butanone (300) than had been determined earlier by conventional methods618. 

Extraction of stevia sweeteners from dried leaves can be accomplished with acetonitrile in the presence of calcium carbonate solution (116) or with boiling water adjusted to pH 9.0 (107). Ahmed and Dobberstein (117) extracted stevioside and rebaudioside A and C from dried leaves of S. rebaudiana in a micro-Soxhlet apparatus. They observed that chloroform/methanol provided the best results, compared to chloroform or to chloroform/methanol/water. Extraction of stevioside, rebaudioside A and C, and dulcoside A can also be performed by subcritical fluid extraction using C02 and methanol as a modifier. Such an extraction technique has been gaining popularity as an analytical tool because it is rapid, simple, and less expensive in terms of solvent cost (110). Beverages, tabletop sweeteners, beverages containing pulp, and candies are prepared as indicated in Sec. I.C (110,115,118). 

M Ashraf-Khorassani, LY Taylor, FK Schweighardt. Comparison of supercritical CHF, and C02 and methanol-modified CHF, and C02 for extraction of sulfonamides from chicken liver. J AOAC lnt 79 1043-1049,1996. 

SFE and SFE/derivatization for the extraction of phenols from a coal gasification wastewater have been performed by first collecting the wastewater organics on "Empore" C-18 sorbent discs (8). The sorbent discs were first prepared by washing with methanol and water as per the manufacturer s instructions. A 100-mL sample of wastewater was acidified to a pH <2, 4 mL of methanol was added, and the waters were filtered through the sorbent discs. The discs were then placed in a 2.5 mL cell and extracted at 80°C and 500 atm using pure C02, C02 with 1.0 mL methanol modifier placed in the cell, or C02 with 1 mL of 0.1 M TMPA in methanol placed in the cell. (Extractions using methanol modifier and TMPA derivatization were each performed statically for 5 minutes followed by dynamic extraction for 10 minutes.) No attempt was made to dry the discs before SFE. 

Figure 7. SFE of coal gasification wastewater organics extracted from "Empore" discs using pure C02 (Figure 7a) followed by a second extraction of the same disc with liquid methanol for 16 hours (Figure 7b). The SFE extract obtained using methanol-modified...

Since many herbicides are crop-specific, herbicide concentrations in farmer s fields are routinely monitored to determine herbicide carry-over. Residual herbicides from the previous year adversely affect alternate crops grown to be grown during the subsequent season. There has been a limited amount of literature describing the successful SFE of herbicides such as sulfonylureas, diruron, linuron, and s-triazines spiked on various solid matrices with COj and methanol modified C02 (1,8-11). Summarized here are the differences in recovery of atrazine from an actual farmer s soil sample as a function of extraction temperature and pressure using both CO2 and methanol modified COj. Also shown are comparisons of recoveries from real vs. spiked samples and also static vs. dynamic modifier addition techniques. 

When a continuous flow of 5% methanol modified C02 was used for extraction at 60°C/5000psi, an 85% recovery of atrazine was observed, an increase of 38% over the static modifier method and a recovery very close to that observed with a spiked sample. 

A limitation to the use of modifiers in SFC has been the detector compatibility of the specific modifier. For example, most modifiers (i.e. methanol) provide a flame ionization detector response preventing use at a large concentration. In SFE, however, this limitation does not exist since modifiers can be used in a mixed mode with CCb and the sample. Figure 1 (taken from reference 25) shows an example of the use or modifiers in SFE. Here the comparison of extraction efficiencies obtained using CO and CO2 modified with methanol is shown. The matrices extracted in these SFE experiments were an XAD-2 sorbent resin and soils. The target analytes were dibenzo[a,i]-carbazole, diuron, 2,3,7,8-tetrachorodibenzo-p-dioxin (TCDD) and linear alkylbenzenesulfonate (LAS) detergent. For each of these respective analytes the extraction efficiency increased dramatically with the use of C02/methanol modifier compared to pure CO2 only as the extracting fluid. This was even the case for the ionic compounds namely, the linear alkylbenzenesulfonates (LAS), which were quantitatively recovered. 

Combination of static subcritical water extraction and solid-phase microextraction Comparison of CHC1F2, N2O and CO2 extractants. CHC1 F2 gave highest recovery, methanol-modified CO2 gave 90% recovery Combination of supercritical fluid extraction with off-line Fourier transform infrared spectroscopy... 

McNally and Wheeler [364] used supercritical fluid extraction coupled to supercritical fluid chromatography to determine sulfonylurea herbicides in soil. Klatterback et al. [365,366] used supercritical fluid extraction with methanol-modified carbon dioxide followed by high-performance liquid chromatography with UV detection to determine sulfonylurea herbicides obtained on a Cis solid-phase extraction disc. Alternatively the determination was carried out by gas chromatography of the dimethyl derivatives of the sulfonylurea herbicides, employing an electron capture or a NP detector on the gas chromatograph. 

The solid sample is placed in the preheated extraction thimble, and the modified CO2 is added to the desired extraction pressure. The system is held static at the extraction temperature and pressure. At the end of the period, the system is vented into a collection vial containing chloroform. This is followed by a dynamic flush of the system with the CO2 solvent at the same temperature and pressure. Mercury complexed with fluorinated diethyl-dithiocarbamate was extracted from dried aquatic plant material with 95% efficiency by methanol-modified CO2. 

Instead of using a mixture of chloroform and methanol, the extraction of lipids by a mixture of hexane and acetone (2 1) is recommended. This mixture has almost all desirable extraction properties and is superior to the other mixtures with respect to the undesirable properties of these. However, this method for lipid determination is very time consuming. Therefore, in the following section, a fast and easy method for the determination of the lipid content of fish on a fresh weight basis by the modified procedure of Ernst et al. [45], Beck and Mathar [46], and Schmitt et al. [47] is described. 

The use of modifiers occasionally improves the extraction process. Water as extractant can be modified with organic solvents such as methanol, acetone or acetonitrile in low proportions (< 5%) in order to decrease its dielectric constant — and hence its polarity — without the need for a drastic temperature increase [37]. Also, an acid or base can be used to alter the pH in those cases where it significantly influences the extraetion yield [29,46]. On the other hand, surfactants facilitate the extraction of non-polar compounds by formation of micelles [47]. Modifiers are less frequently used with extractants other than water. One example is the addition of sodium acetate to methanol to extract organotins (OTs) the additive increases the efficiency in two ways, namely (a) acetate ion by complexing OTs and (b) sodium ion through cation exchange of OTs sorbed to the clay fraction of sediments [21]. 

For the microbial assay, lipids were extracted using a single phase chloroform/methanol/water extraction after Bligh Dyer (1959) as modified by White et al. (1979) to include a phosphate buffer. The total lipid was fractionated into neutral lipid, glyco-lipid and polar lipid fractions by silicic acid column chromatography (SACC) (Parker et al., 1982 White et al., 1983) using the three solvents of increasing polarity (chloroform, acetone and methanol). The polar lipid fraction (PLFA) was... 

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