Speciation strategies

Since there are few species-specific measuring techniques (see Section 2.2.2), most speciation schemes involve two major operations, namely, separation of the species of interest from the matrix and evaluation of the element content in the separated fractions. 

The alternative approaches to separation fall into a number of general categories such as differentiation between species based on size or charge/size effects chromatographic processes solvent extraction and selective chemical reactions. These topics have all been discussed in preceding sections. 

For analysis of the separated fractions, the techniques used need to be highly sensitive, and preferably reasonably selective, i.e. interference effects should be minimal. Analytical techniques possessing these attributes have been mentioned in earlier sections, and are re-listed (in conjunction with separation modes) in Table 2.7. It will be noted that the number of alternative approaches available is somewhat limited. 

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It is important to note that the application of electrochemical methods to the analysis of samples of art objects and archaeological artifacts allows much more than only simple identification of certain constituents advanced methods of speciation may provide information about constituents that are only slightly differing in then-composition, or for which there are only slight differences in the matrices in which the components are embedded. Further, redox speciation—and in the case of solid samples, phase speciation—can be used to derive information on production processes or corrosion (deterioration) of the components in the time that passed since their formation. The second part of this chapter is devoted to illustrating the capabilities of advanced speciation strategies. 

Implementation of various speciation strategies in flowing systems Enrichment via gold-trap collection Speciation between inorganic mercury and organomercurials... 

Other pattern recognition strategies have been used for bacterial identification and data interpretation from mass spectra. Bright et al. have recently developed a software product called MUSE, capable of rapidly speciating bacteria based on matrix-assisted laser desorption ionization time-of-flight mass spectra.13 MUSE constructs a spectral database of representative microbial samples by using single point vectors to consolidate spectra of similar (not identical) microbial strains. Sample unknowns are then compared to this database and MUSE determines the best matches for identification purposes. In a... 

Many analytical strategies and methods have been described for elemental speciation. However, the so-called hyphenated (coupled or hybrid) techniques. 

Some changes in chapter authorship have occurred since the first edition for a variety of reasons. Chapter 2, General Strategies for Speciation has been left... 

The aim in this contribution is to introduce the reader to some of the alternative experimental strategies that have been used to study two particular categories of inorganic chemical speciation, namely ... 

The various strategies and methodologies for element speciation are discussed in depth in the first part of this book, Techniques for Speciation . This chapter deals with current trends and recent developments in techniques and with recent examples of their application in different compartments of the environment. It also presents recent studies on the speciation of a group of biologically important elements. 

Dietz, Ch., J. Sanz, E. Sanz, R. Munos-Olivas, and C. Camara. 2007. Current perspectives in analyte extraction strategies for tin and arsenic speciation. J. Chromatogr. A 1153 114—129. 

The most frequent, reliable approach for element speciation in real samples today uses combined - or hyphenated - techniques, where species are selectively separated (e.g., by a chromatographic technique) and then the elements in the various chemical forms are selectively detected. To enhance the quality of measurements, molecule-selective detection is also coupled to separation devices. These combinations provide extended flexibility and broad applicability. Disadvantages are that, as complexity increases, the risk increases of system failure. Besides, species equilibrium can be drastically altered during separation due to dilution, some components can be removed, and so on. Under such conditions, species transformation and destruction is a likely consequence. Therefore, the total separation time should be shorter than the transformation rate of species. Figure 17.1 gives an overview of the strategy and various speciation methods mostly used for element speciation in human milk. 

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