And concentration technique

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

More than in the past, a systematic setting of priorities is advocated by the authorities. Development takes place by two approaches (1) an effect-oriented approach and (2) a source-oriented approach. These approaches are based on two issues (1) Which effects are caused by which products-processes (2) Which sources emit-discharge which products In this regard, the scheme from emission to toxicological effect must be traced and concentration techniques must be developed. The close connection between chemical and biological characterization must be strongly stressed in this respect. 

Rappe (25) summarized all the literature with regard to the analysis of polychlorinated dioxins and furans and concluded that, with the standards now available, isomer-specific analyses can be performed for all toxic PCDD and PCDF isomers. However, some attention still has to be focused on characteristics of analytical and concentration techniques that can be promising for the future (26). 

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. 

DeMaio, W., Di Bussolo, J. M., Lloyd, T., Kandoussi, H., and Talaat, R. E. (2005). On-line extraction and concentration techniques using turbulent-flow hplc to analyze human... 

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). 

These cleanup and concentration techniques may be used individually, or in various combinations, depending on the nature of the extract and the analytical method used. 

Jagella, T. and Crosch, W. (1999a) Flavour and off flavour compounds of black and white pepper (Piper nigrum L.). I. Evaluation of potent odorants of black pepper by dilution and concentration techniques. European Food Research and Technology 209(1), 16-21. 

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 separation and characterization of submicron-sized particles in water is difficult, in particular because of artifacts from sampling and concentration techniques. Lead et al. (1997) have presented a critical review of the different techniques for separation and analysis of colloids (filtration, dialysis, centrifugation, but also volta-metry, gels (DET/DGT), field-flow fractionation, SPLITT). Ultrafiltration membranes have been developed with nominal cutoff sizes ranging from the thousands of daltons (Da) to hundreds of thousands of daltons, which have been used to separate the colloidal pool into several fractions. 

Liquid-liquid extraction has for many years been the main extraction and concentration technique in the analysis of organics in water. The... 

Recently, SPME has provided many improvements as the cleanup step of complex samples, particularly for the analysis of volatile compounds by headspace techniques [8]. SPME is a solventless extraction and concentration technique which has advantages as a simple and economic technique that reduces health hazards and environmental issues. 

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. 

Solid-phase microextraction (SPME) is a sampling and concentration technique used to increase the sensitivity of HS methods. This technique is utilized for arson analysis and environmental monitoring purposes and also for clinical and forensic procedures. Short, narrow diameter, fused-silica optical fibers coated with stationary phase polymers are either immersed in the sample or the HS and compounds are adsorbed or absorbed (depending on... 

Development of the extraction and concentration technique for sea water samples. 

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. 

To obtain reliable data, the best course is to separate the analytes from the matrix constituents and determine them in the isolated state. This results in greater sensitivity but calls for separation and concentration techniques involving chelating resins, ion exchange, and impreganted resins. 

For other separation and concentration techniques the reader is referred to standard analytical separation texts and current publications in analytical chemical techniques. 

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