Extraction methods, comparison

To further validate the assay for use with environmental samples, water samples spiked with molinate were extracted and analyzed by ELISA and GC. Recovery comparisons were made between ELISA and GC for both liquid-liquid and solid phase extraction methods. Recoveries were greater than 90 for levels as low as lppb for all analysis and extraction method comparisons (23.). This study also described the utility and compatibility between solid phase extraction and ELISA for measuring low concentrations of molinate. As much as 10 acetonitrile/propylene glycol (1 1) or 5 methanol had no effect on the molinate assay. Details of this study were reported by Li et al. (38). 

COMPARISON OF MICROWAVE ASSISTED EXTRACTION METHODS FOR THE DETERMINATION OF PLATINUM GROUP ELEMENTS IN SOIL SAMPLES BY ELECTROTHERMAL ATOMIC ABSORPTION SPECTROMETRY AFTER PHASE SEPARATION-EXTRACTION... 

The most common method to extract xylan is the alkaline extraction. Several pretreatment methods can be used in association in order to break the covalent bonds that exist between xylan and other carbohydrates during the extraction (Wang Zhang, 2006). A number of articles studied the use of ultrasound on the xylan extraction. Hromadkova and coworkers reported that 36.1% of xylan was extracted from corn cobs with 5% NaOH solution at 60°C for 10 min of ultrasonication in comparison with 31.5% of xylan in the classical extraction. Both extractive methods yielded xylan with immunogenic properties (Hromadkova et al., 1999). 

Comparison of Figure 4.1.10a and b demonsfrafes fhaf despite the quantitative differences in fhe deduced values, bofh fhe extraction methods yield a similar trend in the range of equivalence ratios investigated. The overall activation energy is observed to peak close to the stoichiometric condition and decrease on both the lean and rich sides. In addition, the overall activation energy values for n-heptane/air mixtures are observed to be lower when compared with iso-octane/air mixtures for all equivalence ratios under consideration. This similarity of trend and the differences in absolute values using two different extraction methods are also observed in the numerical computations with the available detailed... 

The simple and rapid methods include UV-Vis spectrometry, which reveals the presence of a specific colorant according to its maxima in the absorption spectra in an extract by comparison with a reference (pure colorant extract). The identification... 

Table 3.22 Comparison of extraction methods for polyamide samples...

The main characteristics of the ideal extraction method are given in Table 3.47, which at the same time are also criteria for comparison of sample preparation techniques. It is unlikely that a unique best method can be defined, which is analyte and matrix independent. Extraction is affected by polymer functionality, molecular weight and cross-linking. Selective extraction of some additives is basically not possible. Hence, the goal of an ideal extraction would be the complete extraction of all additives from the polymer for subsequent chromatographic separation. 

Validation of extraction procedures is frequently lacking. A good assessment of quality assurance implies that the extraction recoveries are verified, e.g. by spiking of standard addition. A major drawback is that the spike is not always bound the same way as the compounds of interest. For the development of good extraction methods, materials with an incurred analyte (i.e. bound to the matrix in the same way as the unknown), which is preferably labelled (radioactive labelling would allow verification of the recovery), would be necessary. Such materials not being available, the extraction method used should be validated by other independent methods, e.g. by verification against known samples and by use of a recovery SPC chart. A mere comparison of extraction methods is no validation. 

V. Lopez-Avila, Sonication and Soxhlet Extraction in Environmental Analysis Methods Comparison. EPA Report 600/X-93/010, US Environmental Protection Agency Environmental Monitoring Systems Laboratory, Las Vegas, NV (February 1993). 

Sato Y, Sugie R, Tsuchiya B, et al. Comparison of the DNA extraction methods for polymerase chain reaction amplification from formalin-fixed and paraffin-embedded tissues. Diagn. Mol. Pathol. 2001 10 265-271. 

Bruland et al. [122] have shown that seawater samples collected by a variety of clean sampling techniques yielded consistent results for copper, cadmium, zinc, and nickel, which implies that representative uncontaminated samples were obtained. A dithiocarbamate extraction method coupled with atomic absorption spectrometry and flameless graphite furnace electrothermal atomisation is described which is essentially 100% quantitative for each of the four metals studied, has lower blanks and detection Emits, and yields better precision than previously published techniques. A more precise and accurate determination of these metals in seawater at their natural ng/1 concentration levels is therefore possible. Samples analysed by this procedure and by concentration on Chelex 100 showed similar results for cadmium and zinc. Both copper and nickel appeared to be inefficiently removed from seawater by Chelex 100. Comparison of the organic extraction results with other pertinent investigations showed excellent agreement. 

Table 2.2 shows a comparison of various extraction methods for solid samples [17]. It appears that one can take anywhere from 0.1 to 24h for the extraction process. Microwave-assisted sample preparation requires minimal time however, if cost is a consideration, Soxhlet extraction is least costly but requires the longest sample preparation time. 

The main comparisons between extraction methods have been made between the Soxhlet, ultrasonication, and supercritical fluid extraction [377, 398,456,461,462]. This has primarily been prompted by the need to evaluate critically the relative merits of SFE as an alternative to the more established methods. Richards and Campbell [456] made a comparison between SFE, Soxhlet, and sonication methods for the determination of some priority pollutants in soil. The SFE apparatus was the same, relatively standard system as described by Campbell et al. [457] with the addition of a C02 cryogenic trap to... 

A nnmber of phenolic snbstances were identified by Sterbova et al. [363] in different plants by a BDS C18 colnmns with 3 pm particle size, and a comparison was carried out on different extraction methods, by the comparison of microwave-assisted extraction (MAE) to the traditional approach. 

A comparison of extraction methods for primary aromatic amines including 1,4-phenylenediamine, 2,4-diaminotoluene, benzidine, 4,4 -methylenebis (2-chloroanilme), 3,3 -dimethylbenzidine, and 3,3 -dichlorobenzidine from solid matrices was conducted. Supercritical fluid extraction (SEE) was evaluated and compared with the classical method, sonication extraction (Oost-dyk et al., 1993). 

Fawkes J, Albro PW, Walters DB, et al. 1982. Comparison of extraction methods for determination of polybrominated biphenyl residues in animal tissue. Anal Chem 54 1866-1871. 

For a compound to contribute to the aroma of a food, the compound must have odor activity and volatilize from the food into the head-space at a concentration above its detection threshold. Since aroma compounds are usually present in a headspace at levels too low to be detected by GC, headspace extraction also requires concentration. SPME headspace extraction lends itself to aroma analysis, since it selectively extracts and concentrates compounds in the headspace. Some other methods used for sample preparation for aroma analysis include purge-and-trap or porous polymer extraction, static headspace extraction, and solvent extraction. A comparison of these methods is summarized in Table Gl.6.2. 

A first approach to analyze such volatiles is the application of the AEDA on extracts prepared by dynamic headspace extraction. An apparatus used for the extraction especially of solid foods is shown in Figure 5 [55]. The powdered material is placed into a rotating cylinder and the volatiles are continuously flushed onto a polymer material (Tenax( )) by using a stream of helium (1 L/min). After 3 hr the volatiles are desorbed from the polymer by elution with a small amount of diethyl ether and evaluated by AEDA after concentration. Since different yields may change the composition of the volatiles during headspace extraction [7], it is essential to sensorially evaluate the flavor of the extracts in comparison with the food flavor itself. The following examples show applications of this method on fresh and stored wheat bread crust [55] and on fresh rye bread crust [P. Schieberle and W. Grosch, unpublished results]. 

A comparison has been made between SFE and Soxhlet extraction methods in regards to recovery of analyte, speed of extraction, and relative cost per extraction (15). Such comparative studies are dependent, as is our study, not only upon the extraction conditions used but upon the type and cost of the equipment. The investigation described in this paper compares SFE with standard Soxhlet methods in terms of extraction time, analyte recovery, method simplification, environmental hazards, portability, and cost per extraction using a commercially available SFE system. 

Majority of the sampling techniques described in the literature involve the direct analysis of pieces of cheese, with the primary aim of simplifying the procedure and reducing the analysis time. Our research group has believed that in order to fully tap the potential of FTIR spectroscopy, minimize interferences from the cheese matrix, and successfully analyze minor compounds, a simple extraction procedure may be required. Several extraction methods were discussed earlier in this chapter. However, none of them were adopted for the FT-MIR analysis of cheese until Koca et ah (2007) analyzed the WSE of Swiss cheese to determine short-chain fatty acids. A comparison of the analysis of WSE with the direct analysis of... 

Comparison of simple methanol extraction, Soxhlet extraction, pressurized liquid extraction (PLE), and supercritical fluid extraction (SFE) shows (Clausen et al., 2003) that DEHP can be extracted relatively easily from dust and that the effectiveness does not differ significantly between the different extraction methods (see Figure 2.4). Selection of the optimal method depends on several circumstances, for example number of extraction cycles, instrument accessibility and the analysis method. However, PLE using cyclohexane/acetone was chosen as the preferred extraction method in the field study. 

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