The Extraction Technique

Volatile analytes can be separated from a nonvolatile matrix using any of the extraction techniques described in Ghapter 7. Fiquid-liquid extractions, in which analytes are extracted from an aqueous matrix into methylene chloride or other organic solvent, are commonly used. Solid-phase extractions also are used to remove unwanted matrix constituents. 

Other kinds of bloassays have been used to detect the presence of specific allelochemical effects (8), effects on N2 fIxatlon (9), the presence of volatile compounds (10) and of Inhibitory substances produced by marine microalgae (11). Putnam and Duke (12) have summarized the extraction techniques and bioassay methods used In allelopathy research. Recent developments In high performance liquid chromatography (HPLC) separation of allelochemlcals from plant extracts dictates the need for bloassays with sensitivity to low concentrations of compounds contained In small volumes of eluent. Einhellig at al. (13) described a bloassay using Lemna minor L. growing In tissue culture cluster dish wells that maximizes sensitivity and minimizes sample requirements. 

Hinman et al. [492] have compared SFE and ASE in the extraction of antioxidants from LDPE. Comparable extraction yields were obtained with both techniques. However, sample clean-up was necessary after ASE , while with SFE the extract could be analysed directly without any post-extraction clean-up. Supercritical fluid extraction of 15 polymer additives (AOs, UVAs, process lubricants, flame retardants and antistatic agents) from eight PS formulations was compared to dissolu-tion/precipitation extractions [557], Additive recoveries were comparable. Numerous additional comparisons can be found under the specific headings of the extraction techniques (Sections 3.3 and 3.4). 

Significant differences at the 99% confidence level were observed for the extraction technique and for the polyaromatic hydrocarbons concentration in the soil. The average recovery by the Soxhlet technique was 74.5% whereas 62.8% was the average Polytron recovery. A much higher proportion was extracted with polyaromatic hydrocarbons at the 50pg/g level (72.6%) than at the 5pg/g level (64.6%) suggesting that the extraction efficiency is not constant with concentration. 

Natural colours include annatto, anthocyanins, beetroot red (betalaines), caramel, carotenoids, cochineal and lac pigments, flavanoids, chlorophylls and tumeric. There is a trend towards encapsulating natural colours for food use, but this is not yet reflected in the extraction techniques described in the published analytical methods. Lancaster and Lawrence (1996) described the extraction and... 

The extraction technique can play an important role in the recovery of volatiles, resulting in different profiles of volatiles for the same variety [67]. The direct extraction of Cucumis melo L. var. cantaloupensis with Freon 11 under low temperature was capable of recovering compounds never found before in melons [26]. The authors attributed this to the non-destructive extraction at low temperatures and the very efficient capillary chromatographic system used for the analysis. 

Solvent extraction is an excellent choice for aroma-compound isolation from foods when applicable. Unfortunately, many foods contain some lipid material, which limits the use of this technique since the lipid components would be extracted along with the aroma compounds. Alcohol-containing foods also present a problem in that the choice solvents (e.g. dichloromethane and diethyl ether) would both extract alcohol from the product, so one obtains a dilute solution of recovered volatiles in ethanol. Ethanol is problematic since it has a high boiling point (relative to the isolated aroma compounds), and in concentration for analysis, a significant proportion of aroma compounds would be lost with the ethanol. As one would expect, the recovery of aroma compounds by solvent extraction is dependent upon the solvent being used, the extraction technique (batch or continuous), and the time and temperature of extraction. 

Of the vitamin A commonly found in foods, only all-tran.v-retinol and smaller amounts of 13-ds-retinol, both in esterified form, are usually present in significant quantities. For the analysis of vitamin A-fortified foods, HPLC can be applied to determine either the total retinol content or the added retinyl ester (acetate or palmitate), depending on the extraction technique employed. 

To get the most out of the HPLC as a time machine, we have to analyze the separation, then put to work the extraction techniques we have discussed to speed the separation. As an example, we will take a metabolite study carried out by one of my customers. His problem was to study the dispersion of a compound, XX, in the environment. He had to follow its fate and metabolites in samples of water, sludge, soil, and fish tissue. 

The conclusions that can be drawn from the work presented in this chapter emphasize the miniaturization trends currently being pursued in modern analyte extraction techniques. The trends are focused mainly on miniaturization of the core idea of the extraction techniques utilized for analyte extraction from water samples. This has in turn promoted automation and hyphenation of extraction principles with on-line or off-line connection to analytical instruments. 

A rather simple and convenient method to separate methyl alcohol and trimethylborate is the extraction technique. Since trimethylborate is highly reactive, its extraction requires well-purified oils, e.g. salve base. Salve base is a highly convenient agent, since it practically does not dissolve methyl alcohol in the presence of trimethylborate the solubility of methyl alcohol increases in proportion to the trimethylborate content. 

Bianchi and Vlahov, 1994). Furthermore, as has been pointed out in many research papers, some of these minor components are determinant factors of oil stability, as well as being relevant from the hedonistic and salutary points of view (Table 2.1). The natural concentration of these minor components in an oil can vary greatly, being related mainly to the cultivar, the stage of maturity of the fruits, the soil, the climate and also to the extraction technique adopted (Kiritsakis and Christie, 2000). 

It is concluded from the characterization studies, that the extraction technique which we have employed for the preparation of zeolite-supported iron catalysts results in the formation of highly dispersed, small particle-sized Y-Fe2°3 on the support surface and, in addition, a small amount ( 1%) of iron present as a spe-... 

Catalytic Evaluation In order to investigate support effects in these iron/zeolite catalysts prepared from Fe3(C0)12 by the extraction technique, three catalysts of similar weight percent iron loading were evaluated for their ability to catalyze synthesis gas conversion these catalysts were 15.0% Fe/ZSM-5, 16.4% Fe/Mordenite andl5.0% Fe/13X. All catalysts were evaluated under similar conditions as described in the experimental section. Catalytic data is presented in the accompanying figures in each figure the first three points for each catalyst are data obtained at 280°C, the second three points are data at 300°C. 

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. 

One of the most crucial considerations in proteomic analysis is sample preparation because this will ultimately dictate the number and type of proteins that can be processed. The first priority is to establish the precise protein system to be studied [e.g., will this be a comprehensive and exhaustive catalogue of every expressed protein within a tissue or cellular extract, or is only a small subset of a cellular proteome (e.g., only phosphoproteins or membrane-bound proteins) sufficient for analysis ]. Whether a full or partial proteome, or even a limited number of specific proteins is required for analysis, it is crucial that the extraction technique provide maximal protein recovery while preserving the integrity of the protein complex to be examined. Furthermore, the method of preparation must be totally compatible with the separation methods to be used. This is particularly important for separation technologies that are reliant on protein-protein interactions or drug/ligand/antibody, etc. interactions. Poor recovery of proteins is clearly... 

The isolation of microcystins by SFE is effective and successful. However, the main drawbacks of SFE are the difficulties in a tedious optimization of SFE methods, as several parameters need to be considered with this technique. In addition, because of the high investment cost of the technique, economic considerations will, in practice, also influence the choice of the extraction technique. Yet future trends will depend on the availability of commercial apparatus. 

This step can be included in the extraction techniques because, in most of the cases of extraction, the analytes are being transformed. This step is only necessary for analytes that cannot be determined directly in the form that they already exist in solution. In the SIA system, the derivatization process can be assimilated with a reaction between analyte(s) and reagent with the optimum parameters for both the reaction and SIA system [8,10] the difference is that the product of the reaction is not channeled to the detector, but is channeled to the chromatograph. 

The contribution of the variance of the atomic absorption analysis to the total variance was calculated from duplicate AA analyses of the same extract, usually at the beginning and end of a series of AA measurements of a single metal. The variance of the AA method and the variance of all other factors, including the extraction itself, were calculated and are presented in Table VIII. It can be observed that the contribution to the total variance by the AA measurement is substantial for Cd, Ni, Pb, and Zn. The relative standard deviation from other sources, including the extraction technique itself, contamination, and variation between sup-... 

The challenges inherent in the analysis of gas bubbles trapped in the ice were reviewed by J. Chappellaz (84). The gas, in fact, should be extracted without losses or contamination and the minute amounts available require sophisticated analytical approaches. On the other hand, unique information can be gained in this way on the composition of the atmosphere as far back as 100,000 years ago. The extraction techniques employed are basically dry extraction, melt extraction and sublimation. Past changes in greenhouse gases can be reliably documented so that global biogeochemical cycles can be better understood. 

As an alternate IR assay, accurately weigh about 150 mg. of sample and USP Propoxyphene Hydrochloride reference standard. Quantitatively transfer both to 50 ml. volumetric flasks and dilute with chloroform. Read both at the maximum (about 5 75 M-) with chloroform as the blank, using 1 mm. cells and a suitable spectrophotometer. The calculation is the same as for the "extracted" IR assay. For a true measure of propoxyphene hydrochloride content in a sample, the extraction technique is better. The extraction technique removes many (if not all) of the acidic contaminants which absorb in the carbonyl region. 

The extraction techniques in current use in most laboratories throughout the world are still based on the kaolin-acetone procedures of Albert (A2) and Loraine and Brown (L8) or the tannic acid method of Johnsen (Jl). There is little information in the literature regarding the reliability criteria of these methods. Loraine and Brown tested the accuracy of their kaolin-acetone method in a series of recovery experiments in which a reference material prepared from urine, HMG-20A, was added to urine and recovered the end point of the bioassay was the mouse uterus test for total gonadotropic activity. The mean percentage recovery was 76,... 

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