Recovery extraction method 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). 

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. 

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. 

The use of SFE and MAE has been generalized to many essential oils and different samples. These techniques have improved recoveries in the determination of most organic additives, as well as permitted considerable reductions in solvent volume and extraction time. However, the comparison of extraction methods was usually reduced to relative recoveries of target analytes, ignoring important analytical parameters of the method. Selectivity is one of these, as the coextraction of other organics from the matrix usually requires a postextraction cleanup step before chromatographic analysis. There is still much effort to be carried out in this field in order to optimize the extraction of essential oils from different natural matrices. The selection of the best extraction method depends on the components to be extracted, and this is something to be carefully considered in each particular case. 

Comparison of optimized SFE with a 24 hour Soxhlet extraction in terms of percent recovery, extraction time, and reproducibility shows significant differences. Both methods showed comparable recoveries (e.g. SFE = 94% relative to Soxhlet). An obvious advantage of SFE (1.5 hours) over Soxhlet (24 hours) lies in the time required for extraction. SFE (relative standard deviation, RSD = 2.5%) was also more reproducible than Soxhlet extraction (RSD= 3.4%) although the mass of the seed extracted via supercritical CO2 was smaller than that extracted by Soxhlet (Ig versus 10 g). 

Comparison of Extraction Methods. Preliminary analytical results (12) indicated that our ambient-temperature tumbler sediment extraction was about as efficient for hydrocarbon recoveries as soxhlet extraction. To test the tumbler extraction performance more completely, we have compared it with an alkaline methanol reflux extraction (13) a 1 1 benzene methanol soxhlet extraction (10) and a 2 1 dichloromethane methanol (azeotrope 7.6 1) soxhlet extraction (15), using replicate analyses of the homogenized harbor sediment. 

A comparison of three extraction methods used for recovery of PAH material from sediments showed that the CH2C12 reflux and the soxhlet extraction were approximately equal in their ability to extract PAH material however, ball-mill tumbling was only approximately 72% as efficient. The similarities of the AHDs and PCDs obtained from the three extraction methods indicate that any of these methods could have been utilized to characterize the PAH assemblages in the sediment but these findings... 

Determination, offline GC-FlD samples are allowed to age (up to 42 days) and periodically extracted samples ageing leads to a recovery decrease due to a development as strong interactions between CVAA and matrix active sites, as time elapses comparison between three extraction methods. ... 

Solid-phase micro-extraction (SPME) first became available to analytical researchers in 1989. The technique consists of two steps first, a fused-silica fiber coated with a polymeric stationary phase is exposed to the sample matrix where the analyte partitions between the matrix, and the polymeric phase. In the second step, there is thermal desorption of analytes from the fiber into the carrier gas stream of a heated GC injector, then separation and detection. Headspace (HS) and direct insertion (DI) SPME are the two fiber extraction modes, whereas the GC capillary column mode is referred to as in-tube SPME. The thermal desorption in the GC injector facilitates the use of the SPME technology for thermally stable compounds. Otherwise, the thermally labile analytes can be determined by SPME/LC or SPME/GC (e.g., if an in situ derivatization step in the aqueous medium is performed prior to extraction). Different types of commercially-avarlable fibers are now being used for the more selective determination of different classes of compounds 100 /rm polydimethylsiloxane (PDMS), 30 /rm PDMS, 7 /rm PDMS, 65 /rm carbowax-divinylbenzene (CW-DVB), 85 /rm polyacylate (PA), 65 /rm PDMS-DVB, and 75 /rm carboxen-polydimethyl-siloxane (CX-PDMS). PDMS, which is relatively nonpolar, is used most frequently. Since SPME is an equilibrium extraction rather than an exhaustive extraction technique, it is not possible to obtain 100% recoveries of analytes in samples, nor can it be assessed against total extraction. Method validation may thus include a comparison of the results with those obtained using a reference extraction technique on the same analytes in a similar matrix. 

A comparison of sonication and Soxhlet extraction methods was made by Lopez-Avila et al. ° EPA methods 3550 and 3540 were used to extract some phthalate esters from solid samples, such as sandy loam soil and municipal sludge. The mean recoveries for the method 3540 (Soxhlet extraction) were, in general, similar to those obtained for method 3550 (ultrasonic extraction) however, its RSD was much higher. 

For the analysis of solid tissue samples such as muscle, kidney, or liver, a representative liquid sample first has to be obtained. Fluids can be simply collected by the fluid expression technique (Section 5.2.4). To improve detection limits for certain compounds and provide an alternative method for samples where the fluid cannot be obtained by expression alone. Stead et al. described a solvent extraction method applicable for the generic recovery of antimicrobial compounds from a wide variety of matrices. A comparison of the fluid expression and solvent extraction techniques in combination with the... 

For the comparison of the performance of ASE with commonly used extraction methods such as SE and MAE, standard-spiked PUF and filter samples were processed separately. An overall comparison between the recoveries is shown in Fig. 3, in which the individual bars represent the average values obtained from triplicate measurements for each target compound. All extraction techniques used the HEX/ACE solvent composition and the optimized extraction time and temperature (for SE and MAE, the optimum conditions are from the literamre). The recoveries of SE even after 8 h extraction were significantly lower than those of MAE (20 min) and ASE (40 min 2 cycles x 20 min/cycle) for both PUF and filter samples, respectively. Although MAE and ASE-1 cycle achieved similar efficiencies, ASE-2 cycles gave the best recovery for all target compounds. Furthermore, good reproducibility was also obtained for ASE, which is most likely due to the automation of the whole extraction procedure. 

The use of these alternative extraction techniques has been generahzed to many essential oils and different samples as previously mentioned. These techniques have improved recoveries in the determination of most organic additives, as well as permitted considerable reductions in solvent volume and extraction time. However, the comparison of extraction methods was usually reduced to relative... 

To calculate the molar ratio of the gene products of an operon it is necessary that the number and identity of the subunits of each enzyme be known and that reliable enzyme assays be performed on crude extracts. A comparison of the quantity of enzymes obtained after purification is not a reliable method of obtaining such information, since variations in recoveries render these quantities meaningless in terms of the in vivo molar ratios. Although employing crude extracts overcomes this difficulty, it raises other problems. For instance, precautions must... 

UV method was reported as an effective technique for the determination of the natural DON in seawater samples [56,80], even if some reference compounds containing N-N and N=N bonds were found clearly recalcitrant to UV oxidation. In contrast, [40] reported poorer recoveries of TDN in natural seawater samples and in reference materials by UV method compared to HTO and PO methods. The effectiveness of UV method was also controversially debated in the case of the analysis of nitrogen in rainwater samples and water-extracted aerosols [116-119]. Broad method comparisons of the different techniques for TDN analysis [148,151] showed that UV method can give comparable N-recoveries with respect to the other methods, although its precision seems to be lower, probably because of some uncertainties due to the colorimetric determination of the final inorganic nitrogen products. The low blank of this method and the possibility of the simultaneous determination of DON and DOP were cited as positive factors [40,80]. 

Table 1 shows the comparison of the average recoveries of the four analytes fortified in the soil and incubated for 1 day and 59 days. There was no significant difference between the 1-day and the 59-day periods. This indicates that the analytes do not degrade in the soil at the incubation conditions and are recoverable from the soil. However, the extraction method remains to be tested for long-term-aged soil. 

Traditional techniques, such as Soxhlet, can take 4-48 h. With PFE, analyte recoveries equivalent to those obtained using traditional extraction methods can be achieved in only 15-30 min. Although PFE uses the same aqueous and organic solvents as traditional extraction methods, it uses them more efficiently. A typical PFE extraction is done using 50-150 mL of solvent, see Table 2.6 for comparison. 

Optimization. Optimi2ation of the design variables is an important yet often neglected step in the design of extractive distillation sequences. The cost of the solvent recovery (qv) step affects the optimi2ation and thus must also be included. Optimi2ation not only yields the most efficient extractive distillation design, it is also a prerequisite for vaUd comparisons with other separation sequences and methods. 

Because the protein analyte is endogenous to the plant, it can be difficult to demonstrate the efficiency of the extraction procedure. Ideally, an alternative detection method (e.g., Western blotting) is used for comparison with the immunoassay results. Another approach to addressing extraction efficiency is to demonstrate the recovery of each type of protein analyte from each type of food fraction by exhaustive extraction, i.e., repeatedly extracting the sample until no more of the protein is detected. " ... 

Applications Caceres et al. [114] compared various methods for extraction of Tinuvin 770 and Chimas-sorb 944 from HDPE pellets, namely room temperature diffusion in CHC13 (20 % extraction), ultrasonica-tion (20% extraction), Soxtec extraction with DCM (nonsolvent) (50 % extraction), dissolution (dichloroben-zene)/precipitation (2-propanol) (65-70% recovery) and boiling under reflux with toluene (solvent) at 160 °C (95 % extraction). By changing conditions (nature of solvent, T, t) similar comparisons do not have much added value. Table 3.6 compares the results of reflux extraction and MAE for additives in LDPE [115]. 

A comparison of active (using pumps) and passive (relying on diffusion) sampling techniques for the determination of nitrobenzene, benzene and aniline in air was mentioned in Section IV.A77. Several LLE methods for nitroaromatic compounds dissolved in water were evaluated. High recoveries were achieved with discontinuous or continuous extraction with dichloromethane, adsorption on a 1 1 1 mixture of Amberlite XAD-2, -4 and -8 resins and elution with dichloromethane445. 

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