Extraction techniques summary

Table 3 Summary of solid-phase extraction techniques applied to the preparation of water samples for the determination of triazine pesticides...

In summary, the development of materials for the extraction of pesticides from water samples has progressed from simple liquid-liquid extraction for the principal active compound to sophisticated SPE media capable of exclusively trapping the target pesticide and metabolites selectively. The development of alkyl bonded phase silica cartridges and extraction disks combined with on-line extraction techniques is currently the principal means used for the extraction and trace enrichment of pesticides and metabolites from water. 

Table 3.4 Summary of polymer/additive dissolution and extraction techniques"... 

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). 

More recently, there has been a renewed recognition of the potential of bark-derived polyphenols for adhesives as a result of improved understanding of the chemical structure of these materials (, 5), new types of formulations (5), and the fact that tannins are being commercially used in adhesives in South Africa (7), thus serving as a prototype for utilization in other parts of the world. In order to properly assess the current developments in this field, this overview will provide a historical perspective on adhesives based on tannins as well as a summary of the extraction techniques and chemical structures. Finally, areas where additional work could be fruitful will be suggested. 

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]. 

Since the development of transvenous lead extraction techniques, efforts have addressed the individuation of factors affecting results and incidence of complications. The aim of these efforts was the possibility of evaluating the risk-benefit ratio in individual patients to improve results and reduce possible risks. Many clinical and technical factors may play significant roles in transvenous extraction [2, 37, 58] characteristics of the material to be extracted (lead design, implant site, fixation mechanism, coils, polarity, thickness, insulation), of the patient (sex, age, underlying diseases), and of clinical history (implant time, implant vein, number and position of leads, lead failure or damage) must be evaluated to help predict the outcome of the extraction procedure and to forecast possible complications. A brief summary follows. 

From plots of the distribution ratio against the variables of the system— [M], pH, [HA] , [B], etc.—an indication of the species involved in the solvent extraction process can be obtained from a comparison with the extraction curves presented in this chapter see Fig. 4.3. Sometimes this may not be sufficient, and some additional methods are required for identifying the species in solvent extraction. These and a summary of various methods for calculating equilibrium constants from the experimental data, using graphical as well as numerical techniques is discussed in the following sections. Calculation of equilibrium constants from solvent extraction is described in several monographs [60-64]. 

As a summary of observations on sample preparation of all types, some generalizations can be reiterated. Whenever possible, blank samples spiked with standards should be employed and recovery studies should include assays of each extract, to monitor possible drug-substrate interaction. One technique effective in this regard, is to examine the aqueous phase by TLC after all the "free" drug has been extracted. Standard calibration curves should be compared to similar plots in the presence of sample matrix constituents whenever possible. GC should never be employed as the sole criterion in any analytical evaluation. 

In summary, SPE methods, including extraction using both online and offline cartridges or more automated equipment such as the ASPEK, PROSPECT, or the OSP-2, are, without doubt, the preferred technique for the isolation and concentration of OPPs and OCPs from water samples prior to HPLC determination. 

The marked impact of GC-MS on the analysis of steroids is strongly reflected in the comprehensive volume of published literature on the subject. It has become an indispensible technique for their structural elucidation and identification in extracts of the complex biological mixtures in which they are found. Recent reviews [2,202-204] provide a useful summary of the general progress in the field. 

One of the most commonly used fibers for VOC analysis is coated with a lOO-pm polydimethylsiloxane phase (PDMS) and is available as a unit with a stainless-steel guide rod housed in a hollow septum-piercing needle (Supelco, Bellefonte, PA, USA). The fiber can be withdrawn into the needle for protection during handling and the depth of fiber exposure can be controlled using the adjustable holder. In HS techniques, the needle can be used to pierce the septum of the sample vial and to introduce the fiber into the injection port of the gas chromatograph. In the sample vial, the extraction onto the fiber reaches equilibrium fairly quickly for volatile compounds. Mills and Walker s review includes tabular summaries of HS-SPME-GC methods for the detection of alcohols, drugs, solvents and chemicals in blood and urine. 

In summary, for the determination of single OP compounds in blood or organic tissues, different GC methods in combination with various detection methods (MS, NPD, FPD) are used. For sample preparation, some authors prefer the traditional liquid-liquid extraction, others use SPE on conventional Cig materials. In addition to these methods, novel techniques... 

An overview of PCB analysis, including sampling technique, extraction, cleanup procedures, and quantification is reported in EPA Method 1668 (Revision A EPA 1999k). A summary of representative methods is shown in Table 7-3. The table includes methods that have been standardized by NIOSH,... 

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