Cleaning by Soxhlet extraction

The XAD-4 quaternary resin was cleaned by Soxhlet extraction and kept wet under water to minimize artifacts from the resin. An oily, yellow residue observed during concentration of the acidic eluants required an additional cleanup step. On the basis of the results of the resin blank experiments, it was necessary to clean the XAD-4 quaternary resin by batch process with saturated HCl/methanol prior to Soxhlet cleaning with solvents. Artifacts such as benzoic acid were found in the resin blank experiments, but, in general, the mass of each artifact (per dry weight of resin) was negligible. 

The core experiments with Kern River oil were performed using sandpacks (25.4 cm by 3.7 cm) made from unconsolidated field core. The core material was packed into Teflon sleeves with Teflon end caps and then placed into a Hassler type core holder. Before packing, the sand was cleaned by Soxhlet extraction with toluene and was not fired. Otherwise, the procedure was similar to that for saturating the consolidated Berea sandstone cores. 

Solvents and Reagents. All solvents used in this study were Burdick and Jackson Distilled in Glass. The diethyl ether used was ethanol-free, available from B J on special order. The XAD-2 resins used for sampling the seawater suspensions were purchased from Supelco, Inc., and cleaned by soxhlet extraction according to the method of Junk et al. (17). 

Lee et al. [31] demonstrated that the chlorobenzene and hexachlorobutadiene contents of a lake sediment remained unchanged after four years storage in the dark at 4°C. Subsamples were analysed periodically over the four years by Soxhlet extraction, Florsail cleaning and analysis by capillary column gas chromatography with electron capture or mass spectrometric detection. 

CDFs) addition of 13C-labeled standards followed by Soxhlet extraction with hexane/methylene chloride (1 1) volume reduction and sovent exchange to isooctane columen chromatography on silica gel/potassium silicate/sodium sulfate/celite/sulfuric acid/sodium sulfate volume reduction and solvent exchange to isooctane clean-up using Florisil, carbon/silica volume reduction and addition of internal standard (MID) TCDD) 1994... 

Liquid and gaseous waste effluents (CDDs) Collection of gaseous samples on XAD-2 cartridge followed by Soxhlet extraction with benzene addition of internal standards to liquid samples clean-up and sequential fractionation on basic silica gel/neutral silica HRGC/HRMS (MIM) 1-7.8 pg/m3 (gases) No data (liquids) 94-101 (gases) No data (liquids) Cooke et al. 1988... 

An example is endrin in soil (Fig. 7.7). This highly chlorinated insecticide is extracted by Soxhlet extraction with hexane from a soil that has been mixed one to one with sodium sulfate to remove water. The hexane extract is further dried over sodium sulfate and the hexane is added to a hexane-loaded silica or CN SPE sorbent that has been prepared with hexane. The endrin is sorbed to the silica or CN by normal-phase mechanisms and may be eluted with a solvent that will overcome the interaction, such as methylene chloride or ethyl acetate. The more polar interferences are sorbed to the silica or CN sorbent and are not eluted with endrin. Thus, the SPE column performs both trace enrichment and SPE clean-up. See Chapter 5 for more examples. 

A second approach is to homogenize the sample in some traditional fashion (blender or mortar and pestle) followed by Soxhlet extraction with an appropriate solvent. In this procedure, the solvent is boiled and clean solvent re-extracts the food product each time. This method is effective however, it is quite slow often taking 24 h per sample in order to obtain good recoveries. The analyte must boil at a higher temperature than the solvent for good recovery. Recently, there have been innovations in solvent extraction that combine hot solvent leaching and traditional Soxhlet extraction (Majors, 1996). The sample is first immersed in boiling solvent and then the thimble is raised for... 

The PUF plugs were home-made by cutting them out of a PUF mat which was frozen in liquid nitrogen. The cleaning was first done by repeated water rinsing to remove visible dirt and then for 8 h by Soxhlet extraction with acetone. 

Commercially available silica gel often is not clean enough for application in organic ultra-trace analyses. Silica gel may be cleaned by solvent extraction in a Soxhlet extractor followed by dehydration and activation in a drying cabinet. This method, however, is not without pitfalls as the cleaned product may pick up impurities from the air inside the drying cabinet. A safer and more convenient method involves the use of an extractor as described in Chapter 18. 

Solvent cleaning, as applied to other carbon electrodes, is expected to be an effective, nondamaging method of electrode pretreatment. Several different solvents can be used to clean the electrode surface including acetonitrile, isopropanol, dichloromethane, and toluene. The solvents should first be distilled for purification. Reagent-grade solvents often contain impurities at levels that can cause significant electrode deactivation. AC can be added to the distilled solvents for additional purification. Soak times of 20-30 min should be adequate. The solvent cleaning can also be performed by Soxhlet extraction. 

Residual dinitroaniline herbicides are generally extracted from 10-25 g of air-dried soil samples using organic solvents such as ethyl acetate, acetonitrile, methylene chloride and acetone by sonication, mechanical shaking or Soxhlet extraction. If necessary, the extract is then cleaned by a Florisil column or SPE. The extract is allowed to evaporate completely to dryness and the residue is dissolved in an appropriate volume of the solvent for GC or HPLC analysis. 

The first recommended soil method for oxime carbamates is the method of Honing et al. by HPLC/MS. The LOQ of the method, specifically for aldicarb, methomyl, and oxamyl, is 0.05mgkg. Soil (lOg) is Soxhlet extracted for 16h with acetone-dichloromethane (1 1) using double-thickness cellulose extraction thimbles (80 X 22-mm i.d.). Prior to extraction, the Soxhlet system and the thimbles are cleaned for 14 h by refluxing with methanol. The extracts are removed and concentrated nearly to dryness in a rotary evaporator operating at 35 °C evaporation to dryness... 

It is not uncommon that extraction techniques are unfairly compared. Appropriate interlaboratory studies are few. Soxhlet and sonication extraction (EPA methods 3540 and 3550, respectively) were compared in an interlaboratory study (129 participants) for PCBs in soil. Results from laboratories using Soxhlet extraction were significantly more accurate than those obtained using sonication, especially at higher concentrations, but with equal precision [196]. This is rationalised by the observation that the Soxhlet procedure presents the sample with fresh solvent so that the extraction solvent is never saturated, unlike the sonication procedure. Sonication is very sensitive to the solvent polarity, nonpolar solvents producing considerably less accurate results than polar solvents. It is not as sensitive to clean-up procedures as... 

A method for sediment involves Soxhlet extraction followed by filtration, and concentration to 5 mL. The residue is diluted with water, acidified, extracted with methylene chloride, and then the extracts are dried and evaporated to dryness. The residue is cleaned up on an alumina column. Analysis is performed by GC/NPD. Good recovery (81-97%) and precision (>15% RSD) were reported detection limits were not reported (Muir et al. 1981). 

Sediment Soxhlet extraction clean-up by liquid-liquid partition, alumina column chromatography GC/NPD 81-97 Muiretal. 1981... 

Fish. Solid biota samples, mainly fish, should be quickly killed by liquid N2 [28] or cervical dislocation [32] and kept at low temperatures (— 20°C). Some authors preferred desiccation of the sample at high temperature (70°C) [33,34] or lyophylisation [28]. The extraction and isolation steps would be combined when using lyophylisation and homogenisation, followed by a Soxhlet extraction, usually with MeOH, and a subsequent solid-phase extraction (SPE) clean-up, prior to the quantification. 

Of the analytical procedures used for the determination of LAS in soils (Table 6.7.1), most methods rely on (Soxhlet) extraction with methanol, followed by clean-up on SPE cartridges (RP-C18 and/or SAX) and final quantitative measurements by HPLC—UV/FL. Applying this protocol, detection limits were achieved ranging between 0.05 and 5 mg kg-1 depending on the matrix, the enrichment factor and the optical detection system employed. 

SPE methods with different cartridge packings have been employed for the pre-concentration and clean up of sulfonated azo dyes from waters and soil extracts [110,111], The extraction of solid samples has been carried ont by sonication or Soxhlet extraction and the extracts treated like the water samples. C18 cartridges and columns [111] were used followed by the elution with aqueous organic solvents in the presence of TEA with recovery yields always greater than 65% [93,111], Higher recoveries have been obtained by using C18 columns, pre-conditioned with an ammonium acetate buffer and elnted with methanol [111], The use of styrene-divinylbenzene [93,112], as well as of cross-linked polymeric sorbents with sulfonate functions, was shown to be suitable in the SPE of the more polar componnds [111],... 

The sorbent materials evaluated for each analyte are listed in Table III. (It was necessary to clean some of the sorbent materials to remove impurities prior to use. The cleaning procedure consisted of Soxhlet extraction with an 80 20 mixture of acetone and methanol for 4 h followed by extraction with hexane for 4 h.)... 

Air pumped through glass fiber filter and adsorbent trap filters and adsorbents are Soxhlet extracted with acetone/hexane cleaned-up by column chromatography... 

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