Column separation methods, elemental analysis

On the basis of the preceding discussion, it should be obvious that ultratrace elemental analysis can be performed without any major problems by atomic spectroscopy. A major disadvantage with elemental analysis is that it does not provide information on element speciation. Speciation has major significance since it can define whether the element can become bioavailable. For example, complexed iron will be metabolized more readily than unbound iron and the measure of total iron in the sample will not discriminate between the available and nonavailable forms. There are many other similar examples and analytical procedures that must be developed which will enable elemental speciation to be performed. Liquid chromatographic procedures (either ion-exchange, ion-pair, liquid-solid, or liquid-liquid chromatography) are the best methods to speciate samples since they can separate solutes on the basis of a number of parameters. Chromatographic separation can be used as part of the sample preparation step and the column effluent can be monitored with atomic spectroscopy. This mode of operation combines the excellent separation characteristics with the element selectivity of atomic spectroscopy. AAS with a flame as the atom reservoir or AES with an inductively coupled plasma have been used successfully to speciate various ultratrace elements. 

Apart from the analysis of individual compounds and many industrial products, methods have been developed for the continuous elemental analysis of compounds already separated into components in a chromatographic column methods have also been evolved for the continuous analysis of individual fractions sampled in the course of chromatographic separation. In most instances the purpose of such analyses is the identification of separated products. An excellent review on this subject was written by Rezl [168]. 

Part 1 Chemistry A Practical Subje d , deals with the common techniques used to prepare, purify and identify chemical compounds. It explains how to plan the preparation of a compound. The separation methods — distillation, recrystallization, thin-layer and column chromatography — are introduced. There is also a discussion of identification by elemental analysis, atomic absorption spectroscopy and mass spectrometry. 

There are two noncolumn cleanup methods, one of which uses acid partition (EPA SW-846 3650) to separate the base/neutral and acid components by adjusting pH. This method is often used before alumina column cleanup to remove acid components. The other method (EPA SW-846 3660) is used for sulfur removal and uses copper, mercury, and tetrabutylammonium sulfite as desulfurization compounds. Sulfur is a common interfering compound for petroleum hydrocarbon analysis, particularly for sediments. Sulfur-containing compounds are very common in crude oil and heavy fuel oil. Elemental sulfur is often present in anaerobically biodegraded fuels. Thus, abnormally high levels of sulfur may be... 

The nutritional, chemical, biological, and toxicological properties of a chemical element are known to be critically dependent on the form in which it occurs in food. The recognition of this fact has spurred the development of species-selective (speciation) analytical methods for food additives and contaminants. According to the IUPAC s dehnition, speciation analysis deals with the analytical activities of identification and/or measurement of the quantities of one or more individual chemical species in a given sample [1], The analytical approach is usually based on the combination of a chromatographic separation technique with an element-specif>c detection technique. The former ensures that the analyte compound leaves the column unaccompanied by other species of the analyte element, whereas the latter enables a sensitive and specil>c detection of the target element. Coupled (also called hyphenated) techniques have become a fundamental tool for speciation analysis and have been discussed in many published reviews [2D6]. 

A second extended function of the liquid column chromatography is to preseparate trace amounts of several substances for subsequent quantitative analysis by a selective determination method such as atomic absorption spectrometry (Table 2.3). Here often only a particular degree of separation is achieved. Non separated elements are to be determined with high-selective methods. In most cases an enrichment is combined with these chromatographic methods (Chap. 4). 

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