Isolation and concentration techniques

Isolation and Concentration Techniques Using Physical Methods.739... 

Aroma compounds are present in minute levels in foods, often at the ppb level ( ig/liter). In order to analyze compounds at these levels, isolation and concentration techniques are needed. However, isolation of aroma compounds from a food matrix, which contains proteins, fats, and carbohydrates, is not always simple. For foods without fat, solvent extraction (unit gu) can be used. In foods containing fat, simultaneous distillation extraction (SDE see Basic Protocol 1) provides an excellent option. Concentration of headspace gases onto volatile traps allows sampling of the headspace in order to obtain sufficient material for identification of more volatile compounds. A separate protocol (see Basic Protocol 2) shows how volatile traps can be used and then desorbed thermally directly onto a GC column. For both protocols, the subsequent separation by GC and identification by appropriate detectors is described in unitgu. 

Aiken, G. R. 1985. Isolation and concentration techniques for aquatic humic substances. In Humic Substances in Soil, Sediment and Water Geochemistry, Isolation, and Characterization (G. R. Aiken, D. M. McKnight, R. L. Wershaw, and P. MacCarthy, Eds.), pp. 363—385. 

According to the operational definition, it is most important that well-defined methods and clear protocols are provided describing the isolation procedure applied. After isolation, freeze-drying is often used to stabilize the final fraction and to prevent chemical and biological reactions during storage. Critical reviews on the isolation and concentration techniques for aquatic substances are given by Aiken (1985), Leenheer (1985), and Abbt-Braun and Frimmel (2002). 

Aiken, G. R. (Ed.). (1985). Isolation and Concentration Techniques for Aquatic Humic Substances. Humic Substances in Soil Sediment and Water. Wiley, New York, pp. 363-385. 

The samples were separated by capillary gas chromatography and peak areas compared. The results of that study which are shown in Figure 1 demonstrate that no single isolation and concentration technique is uniformly satisfactory. Rather, the choice of technique is determined by the information desired. They did conclude, however, that distillation-extraction gave results which most nearly agreed with direct injections of the neat mixture. 

The goal of this article is to review current sample isolation and concentration techniques which have value in the analysis of biologically generated aromas. Relatively simple and straightforward techniques will be emphasized since the researcher frequently wishes to analyze a number of samples, e.g., cell cultures, fermentation broths and plant materials, in a short period of time. 

Aiken G.R. (1985), Isolation and concentration techniques for aquatic humic substances, in Aiken G.R., McKnight D.M., Wershaw R.L., MacCarthy P. (Eds.), Humic Substances, in Soil, Sediment, and Water, John Wiley Sons, Inc., 363-386. 

Poole, C.F. Schuette, S. A. Isolation and concentration techniques for capillary column gas chromatographic analysis. J. High Resolut. Chromatogr. 1983, 6, 526-549. 

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