Extraction techniques, comparative studies

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... 

It is generally difficult to identify developments with high potential where interferences do not preclude general application. To ensure the relevance of a method, its application to real sample analysis must be demonstrated. The accuracy of an analytical method should be confirmed by an independent method, or by the analysis of certified reference materials. Detailed comparative studies of the method developed with other well-established methods for polymer/additive analysis are not frequent in the analytical literature. Nevertheless, some examples may be found in Section 3.6. Improvements in analytical techniques are reasonably sought in sample preparation and in hyphenated chromatographic techniques. However, greatest efficiency is often gained from the use of databases rather than accelerated extraction or hyphenation. 

A comparative study of extraction methods from formalin-fixed mouse liver by Jiang et al.11 highlights the importance of sample preparation technique. Formalin-fixed mouse tissue was extracted using five different protocols (1) 6M guanidine-HCl without heating (2) 6M guanidine-HCl... 

As an extraction technique, SFE proved to give comparable recoveries to those of Soxhlet extraction. In all cases, SFE dramatically shortened extraction times and minimized most environmental hazards, solvent concentration steps, and waste disposal costs. A summary of this comparison is included as Table XII and is a projected cost comparison of SFE to Soxhlet extraction, based on our experiences with the SFE system used in these studies (Isco SFE System 1200). The projected cost per extraction was determined to be 15.85(SFE) vs. 22.60(Soxhlet). 

Hubert et al. [101] state that accelerated solvent extraction compared to alternatives such as Soxhlet extraction, steam distillation, microwave extraction, ultrasonic extraction and, in some cases, supercritical fluid extraction is an exceptionally effective extraction technique. Hubert et al. [ 101 ] studied the effect of operating variables such as choice of solvent and temperature on the solvent extraction of a range of accelerated persistent organic pollutants in soil, including chlorobenzenes, HCH isomers, DDX, polychlorobiphenyl cogeners and polycyclic aromatic hydrocarbons. Temperatures ofbetween 20 and 180 °C were studied. The optimum extraction conditions use two extraction steps at 80 and 140 °C with static cycles (extraction time 35 minutes) using toluene as a solvent and at a pressure of 15 MPa. 

The use of supercritical-fluid-extraction techniques in the fractionation of polysiloxanes has been demonstrated by the data presented. The poly-dispersities of the fractions were comparable with those generally attainable only by anionic-polymerization techniques, with which the incorporation of two functional groups is often difficult to attain. The ability to isolate these well-defined fractions will lead to important fundamental studies on structure-property relationships in multiphase copolymer systems. 

Table 31.3 gives a few typical examples on recovery of actinides by ELM. Myriad literature reports exist on the use of HDEHP for metal extraction involve ELMs. Comparative studies between column and batch liquid emulsion membrane techniques based on HDEHP/HCl system were carried out to develop a system for the isolation of Th from natural uranium, which showed that, kineticaUy, the equilibrium for thorium separation using batch technique is faster than the continuous column system [37]. The effective separation of Th from natural uranium was found to be independent of time. El-Sherif studied... 

The validation of the microwave-assisted extraction technique was performed by comparing the values obtained to that of the standard samples and by performing conventional prescribed official methods associated with each products under study. Table 2 presents a summary of data presented in references [19] and [20]. The results demonstrate that, in all cases, the microwave-assisted extraction procedures yielded data that were, for all practical purposes, similar to the accreditation values of fat content obtained for the same samples using conventional official methods. These results support the current trend whereby several microwave-assisted extraction methods are being evaluated for accreditation purposes. This trend is not exclusive to food analysis [27]. 

Table II compares the composition by wei t of Croteau s and Fogerson s neutral lipid extract and our SF extract. The SF extracts were richer in fatty acids as compared to the neutral lipid extract. The SF extracts contained trace amounts of docosanoic acid and eicosanoic acid which were not identified in the neutral lipid extract. Since the paper published by Croteau and Fogerson has no chromatograms, it is not possible to Imow whether all the peaks in their GC-FID trace were identified. In addition, the analytes in the extract were identified by comparing retention times of a standard with the unknown. This method does not permit the unambiguous identification of an analyte because two different analytes can have similar retention time. In our study, the SF extracts were analyzed by GC-MS which is a superior technique compared to GC-FID because the peaks are identified by comparison of the mass spectrum of the peak component to the mass spectrum of a standard from the Wiley library.

Comparative studies involving recent extraction techniques... 

Determination offline GC-MS (1) extraction of the more volatile PAHs, low density and temperature (2) extraction of the less volatile PAHs, higher density and temperature and addition of modifiers (3) purge the system for removing traces of modifier studies comparing SFE to other extraction techniques (Soxhlet, sonication,... 

Determination GC—MS MAE and Soxhlet are compared table with found PCB concentrations by both methods is given recoveries ranged from 98 to 123% with MAE and from 86 to 111% with Soxhlet comparison with other extraction techniques confirmed the efficiency of MAE Determination GC-ECD Three microwave-assisted techniques MAE, microwave- assisted saponification (MAS) and microwave-assisted decomposition (MAD) were studied and combined with success tables with recoveries from studied methods are given Determination offline HRGC-HRMS recoveries ... 

Determination. GC-MS, LOD. 5 to 20 pg Determination. HPLC-UV/FD, MAE with hexane/ acetone (1 1) from real atmospheric particulate samples was investigated and the effect of microwave energy and irradiation time studied Determination, offline GC-ECD/MS the analytes studied are identified at concentration ranging between 10 and 364 pg/m SFE method compared with sonication. good agreement alternative method to conventional extraction techniques such as Soxhlet or sonication... 

D-A complexes are formed by electronic transition from the highest occupied molecular orbital (HOMO) of the donor to the lowest unoccupied molecular orbital (LUMO) of the acceptor. Although /l ax of this transition is not always intense or observed in the visible region, many CT complexes are strongly coloured. This property allows significant structural data to be extracted through comparatively simple techniques including UV/vis spectroscopy, which is one of the factors that facilitated early identification and stmctural studies on these complexes. 

Transient Charge Extraction Techniques A Comparative Study of TOF andCEUV... 

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