Lipids Soxhlet extraction

In some instances, it is desirable to remove lipids and other so-called extractives before proceeding with polysaccharide separation. This removal is generally accomplished through Soxhlet extraction with an azeotropic mixture of ethanol and benzene.26 2 27... 

McLeese et al. [10] studied the accumulation of AP in aquatic fauna including salmon. Fish were mixed with anhydrous sodium sulphate and Soxhlet extracted with ethyl acetate. Lipids were removed by GPC on Biobeads using cyclohexane/dichloromethane (1 1, v/v). The final analysis was performed with GC-FID. The recovery of p-NP was reported as 86%. 

Most existing methods are based on instrumental analysis involving exhaustive sample pretreatment and preconcentration steps, followed by purification and fractionation before final chromatographic separation and detection. For fat and oil samples, dissolving the lipids in an appropriate solvent is usually the first treatment. This has been achieved by melting the fat at 90°C followed by LLE or direct solid liquid extraction (SEE) with an apolar solvent [37], column extraction with a mixture of apolar solvents after drying of the sample with anhydrous Na2S04, Soxhlet extraction and/or sonication with apolar solvents. Typically, sample intake is between 0.5 g and 1 g and quantitative recoveries >60% have been reported. 

The Soxhlet extraction procedure is a semicontinuous process, which allows the buildup of the solvent in the extraction chamber for 5 to 20 min. The solvent surrounds the sample and is then siphoned back into the boiling flask (Fig. D 1.1.1). Multiextractor units are available for extraction of lipids from several different samples or replicate runs of the same material. The procedure provides a soaking effect and does not permit channeling. The fact that polar and bound lipids are not removed is a drawback to the procedure (see Background Information). 

Procedures for isolation and measurement of lipids in foods include exhaustive Soxhlet extraction with hexane or petroleum ether (AOAC, 1995 see Basic Protocol 1), chloro-form/methanol (Hanson and Olley, 1963 Ambrose, 1969), chloroform/methanol/water (Folch et al., 1957 Bligh and Dyer, 1959 see Basic Protocol 2 and Alternate Protocol 2), acid digestion followed by extraction (see Basic Protocol 4), or, for starchy material, extraction with n-propanol-water (e.g., Vasanthan and Hoover, 1992 see Basic Protocol 3). Each method has its own advantages and disadvantages and successful measurement of lipid content is often dictated by the type of sample and extraction medium employed. Commercial extraction and preparation of edible oils are explained in the literature (Williams, 1997). 

In the Soxhlet extraction, usually dry or nearly dried material is subjected to semicon-tinuous extraction with hexane or petroleum ether. The drawbacks of this method are the length of time required for extraction and the fact that polar and bound lipids are not removed, offset by the fact that no channeling occurs. The Goldfisch method, on the other hand, is a continuous process and somewhat... 

Extraction of fat by supercritical carbon dioxide was investigated as an important option for minimizing the expanded use of frequently flammable and carcinogenic solvents in food analysis. Unfortunately, the presence of moisture in foods has an adverse effect on the quantitative extraction of fat by supercritical fluid extraction (SEE). Hence, samples have to be lyophilized first. The total fat content of freeze-dried meat and oilseed samples was found to be comparable to values derived from Soxhlet-extracted samples (26). Besides, only small amounts of residual lipids could be recovered by an additional extraction of the SFE-extracted matrix by the Bligh and Dyer solvent extraction procedure. As far as the minor constituents are concerned, it was found that the extraction recovery ranged from 99% for PC to 88% for PA. Hence, Snyder et al. concluded that SFE can be used as a rapid, automated method to obtain total fat, including total phospholipids, from foods (26). 

Fig. 2. Total lipid in cultured Atlantic salmon (Salmo salar) over their life cycle. Adapted from ref. 123. Data points 1 -8 represent doubling of degree days from fertilization until near hatching 12-26 represent approximate doubling of body weight at each point. Lipids determined gravimetrically after Soxhlet extraction from dried tissues.

Sediments were Soxhlet extracted with acetone/hexane and the extract was concentrated (1 ). Biota samples were extracted by aqueous KOH digestion followed by extraction of non-saponifiable lipids Into ethyl ether ( ). 

Fig. 5 Surface-plasmon resonance curves, i.e., reflectivity-vs-incident angle scans of the bare substrate, a Ag coated glass slide with a thin SiC>2 layer evaporated on top (A), after the self-assembly of a reactive monochlorosilane derivative (cf. Fig. 4a) (B), after the adsorption (from solution), covalent binding, and soxhlet extraction of the polymer cushion (C), and after the deposition of a model lipid monolayer (a layer of reactive ester derivatives of a fatty acid) (D)...

Soxhlet has been developed for the determination of macro-compounds e.g. lipid content in food. It is a more or less continuous extraction procedure and it is regarded as an exhaustive extraction. The idea of an exhaustive extraction is very appealing for both macro and micro pollutants. Therefore overnight extraction i.e. extraction times of 14-16 hours are quite common with Soxhlet extraction. For micro-pollutants, such long extraction times may have some negative implications. This is caused by the non-specificity of any extraction procedure. Suppose that after n cycles, 70% of the available analytes and 10% of the more polar interferences have been extracted. The ratio between wanted and unwanted compounds is then 7. After 2n cycles, the recovery of the analytes has increased to 91% (70+0.7 x 30) but at the same time the interferences have increased to 19% (10+0.1 x90). The ratio between wanted and unwanted has decreased to 4.8. It is clear that infinite extraction will end in an extract with quite a high content of unwanted substances. For the extraction of micro-pollutants, the power of the exhaustive extraction is at the same time its pitfall. 

The procedure for extraction is the same as that described for sediment samples i.e. soxhlet extraction, except for the preparation of the material. The amount of material extracted depends upon the lipid content because the more the fatty material in the tissue the more pre-injection cleanup is required. Thus, for a fish liver sample, about 2g of material is extracted. For muscle tissue, which contains less fatty material, the sample weight can be increased to about 5g. The lipid content is determined on a separate amount of sample by extracting with petroleum ether and evaporating the extract to constant weight over a steam bath. 

The methods for hydrocarbon extraction and analysis are similar to those previously described (16,17,18). Sediment samples were soxhlet-extracted in methanol benzene (1 1) for 48 hr. Copper wool was placed beneath the thimble to facilitate drainage and removal of elemental sulfur. Lipids were partitioned into a pentane-benzene layer (3 combined washes) followed by a wash of saturated NaCl solution, dried overnight with Na2S04, and vacuum-evaporated to dryness. The extract was redissolved in pentane and fractionated by column chromatography on alumina over silica gel (both 5% deactivated with H20). Aliphatics were eluted with three column volumes of pentane, followed by three column volumes of benzene to elute aromatics. Only analyses of the pentane fractions are reported here. 

Determination offline GC—MS the results show that SFE is an appropriate enrichment procedure for soil lipids SFE and Soxhlet extraction give results which are in good agreement... 

The sample was homogenized with anhydrous sodium sulphate and Soxhlet extracted with dichloromethane for 108,109 16 h. Lipids were removed by gel permeation chromatography followed by chromatography on 100% activated silica. PCBs were eluted with n-hexane. Extracts were exchanged into isooctane, and concentrated under a gentle stream of nitrogen for GC analysis... 

Solvent Extraction Studies. Techniques necessary to detect lipid species extracted from in vitro and in vivo exposed Biomer were developed. Extractions with a nonpolar swelling solvent (e.g., CHC13) employing a soxhlet apparatus were performed to extract preferentially lipophilic biological components from Biomer or previously isolated neointimal samples. Experimentation demonstrated the high solubility in chloroform of polymer-derived monomeric and oligomeric components. A separation of lipids from these components was therefore required. 

The effectiveness of solvent extraction was evaluated by a lipid-doped polymer study. Selected lipids were dispersed in Biomer. Then, two sample films, one containing 1 mg, the other 10 mg of palmitic acid, cholesterol, and tripalmitin were cast from two consecutive castings each of 10% Biomer in dimethylacetamide (DMAC). Lipid concentrations of the 1-mg- and 10-mg-doped samples were calculated to be 0.1% and 1%, respectively. Following casting, a soxhlet extraction and quantitative analysis of extracted lipids were performed. The final extracted concentrations were compared with initial solution concentrations, resulting in an extraction efficiency ratio for each type of component. 

Samples were weighed, homogenized and dried with anhydrous sodium sulfate in a mortar (Na SO tissue, 4 1 w/w). They were later transferred to precleaned Soxhlet extraction thimbles (4h-Soxhlett extraction with n-heptane) and internal PCB-standard was added (lUPAC 3, 15, 28, 52, 101, 105, 118, 126, 156, 169, 180, 202, 209, all C. -la-beled nomenclature according to Ballschmiter Zell, 1980). Soxhlet extraction was executed with toluene (50-400 ml, depending on sample weight, ranging from 0.3—98 g). The solvent was evaporated to dryness and the lipid content was determined gravimetrically. 

Sample preparation relied on the specificity provided by NICI and SIM to simplify sample extracts. The fish tissue was spiked with an internal standard, dried with sodium sulfate, Soxhlet extracted with hexane/acetone, and had the lipids removed by deactivated silica gel chromatography. Quantification was based on components with 6-10 chlorine atoms, as these represented the majority of the compounds of toxaphene. The concentrations of the bomane and bomene components were combined because of overlaps of both GC retention times and isotope patterns. 

One of the most interesting fields of application of MAE in food analysis is the extraction of lipids. This step, traditionally performed with conventional Soxhlet extraction, has been performed with the focused microwave-assisted Soxhlet extractor prototype of Figure 2B. Extraction of oil from olives, srm-flower seeds, and soyabeans extraction of the lipid fraction of dairy products (milk and cheese) and extraction of fatty acids from precooked and sausage foods have significant advantages over conventional methods, including dramatically reduced extraction times, lower degradation of thermolabile analytes, and acceleration of other analytical steps such as hydrolysis in milk samples, in addition to completeness of analyte extraction, which is not always achieved with conventional methods. 

Cocoa fat and lipids The lipid components in cocoa are extracted into petroleum ether by either the Knorr Tube method or by Soxhlet extraction. Both are adopted by AOAC, and the latter method by both AOAC and the Office International du Cacao et du Chocolat. In the Knorr Tube method, 2-3 g of cocoa powder or grated chocolate product is transferred into a Knorr Tube fitted with 6 mm of tightly packed mat of washed asbestos filter. The extraction tube is connected to suction by a two-way stopcock, and the stem of the extraction tube is connected to a preweighed Erlenmeyer flask. The extraction tube is filled up to two-thirds capacity by petroleum ether. 

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