Matrix-isolation technique basics

Thus far, we have reviewed basic theories and experimental techniques of Raman spectroscopy. In this chapter we shall discuss the principles, experimental design and typical applications of Raman spectroscopy that require special treatments. These include high pressure Raman spectroscopy, Raman microscopy, surface-enhanced Raman spectroscopy, Raman spectroelectro-chemistry, time-resolved Raman spectroscopy, matrix-isolation Raman spectroscopy, two-dimensional correlation Raman spectroscopy, Raman imaging spectrometry and non-linear Raman spectroscopy. The applications of Raman spectroscopy discussed in this chapter are brief in nature and are shown to illustrate the various techniques. Later chapters are devoted to a more extensive discussion of Raman applications to indicate the breadth and usefulness of the Raman technique. 

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. 

As with all analytical determinative techniques, interelement and matrix interferences exist and accurate quantitative determinations of concentration involve corrections for matrix effects. X-ray spectrometers comprise an excitation source, a means for the separation and isolation of emission lines, a device for intensity measurement, and typically a dedicated computer for calculation and applying corrections. The two basic types are wavelength-dispersive (in which the X-rays are characterized by wavelength) and energy-dispersive (in which the X-rays are measured by their energy levels) spectrometers. A disadvantage, as with many (all) other methods of analysis is the complication caused by the chemical composition of the matrix and as well by granulation, i.e., particle size. It remains the view... 

A challenging task faced by the analytical chemist when dealing with raw samples is extracting/isolating the analyte of interest from the sample matrix. It is fair to say that the majority of nonideal samples arrive in a format incompatible with most analytical instrumentation, and requires some degree of clean-up. Even well-defined samples (e.g. aqueous solutions) require basic filtration prior to analysis. Other desirable techniques may include liquid/liquid extraction and solid phase extraction. 

The analytical techniques used in environmental studies are basically the same as those used in other apphcations, as described in previous chapters. A number of review articles have appeared on the subject (4,8,9). Only rarely can quantitative methods be applied directly to determination of low levels of surfactants in the environment it is first necessary to isolate the materials of interest fix>m the matrix. 

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