Small-scale extractions organic compounds

Analytical methods for monitoring the compounds were developed or modified to permit the quantification of all 23 compounds of interest. As noted earlier, the compounds were initially studied in small-scale extractions by groups. This approach assured minimal interferences in the analyses conducted during the initial supercritical fluid carbon dioxide extractions. Table II summarizes the data on the recovery of organics from aqueous samples containing the compounds of interest at concentration levels listed in Table I when the sample preparation techniques and analytical methods described were used. For each experimental run, blank and spiked aqueous samples were carried through the sample prepration and analytical finish steps to ensure accurate and reproducible results. Analyses of sodium, calcium, and lead content were also conducted on selected samples by using standard atomic ab-... 

From the results of the small-scale tests, a decision is reached as to the most satisfactory method of separation. When the chosen method is applied to the main portion of the mixture, due regard must be paid to technique so as to obtain pure components. Thus, a liquid or solid component obtained by simple separation or filtration must be washed with the solvent used to remove the other component(s). If extraction with a reagent has been used, the component insoluble in the reagent, after its removal, must be washed with the reagent, and traces of the latter removed by a final wash with water. If a component is to be removed with an organic solvent, successive extractions with small portions of the solvent are preferable to a single treatment with a larger volume of solvent. The combined extract is then dried before the dissolved compound is recovered by evaporation of the solvent. 

The preparation of a derivative of a sample compound prior to GC is a significant potential source of both qualitative and, in particular, quantitative errors. Almost all reactions that are used for derivatization are organic syntheses adapted to the micro-scale. This approach makes full use of an advantageous property of GC, namely the need to take only very small amounts of the sample for the analysis, but on the other hand, it makes heavy demands on the quality of the materials used and the precision of the operating procedures. As GC has especially been used in analyses of complex mixtures with large contents of various components, such as biological samples, the operations necessary for the preliminary separation of the compounds of interest from the sample, e.g., extraction or TLC, are often involved in the entire procedure, and make it even more complicated. With some reactions, the necessity for an anhydrous medium requires the application of drying (lyophilization) in the treatment of the sample. 

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