Species speciation analysis

The lUPAC (International Union for Pure and Applied Chemistry) recommends the following definitions for the terms chemical species , speciation analysis and speciation ... 

Today it has become clear that the effect of trace elements in living systems, in food, and in the environment depends on the chemical form in which the element enters the system and the final form in which it is present. The form, or species, clearly governs its biochemical and geochemical behaviour. lUPAC (the International Union for Pure and Applied Chemistry) has recently set guidelines for terms related to chemical speciation of trace elements (Templeton et al. 2000). Speciation, or the analytical activity of measuring the chemical species, is a relatively new scientific field. The procedures usually consist of two consecutive steps (i) the separation of the species, and (2) their measurement An evident handicap in speciation analysis is that the concentration of the individual species is far lower than the total elemental concentration so that an enrichment step is indispensable in many cases. Such a proliferation of steps in analytical procedure not only increases the danger of losses due to incomplete recovery, chemical instability of the species and adsorption to laboratory ware, but may also enhance the risk of contamination from reagents and equipment. 

The list of elements and their species listed above is not exhaustive. It is limited to the relatively simple compounds that have been determined by an important number of laboratories specializing in speciation analysis. Considering the economic importance of the results, time has come to invest in adequate CRMs. There is a steadily increasing interest in trace element species in food and in the gastrointestinal tract where the chemical form is the determinant factor for their bioavailability (Crews 1998). In clinical chemistry the relevance of trace elements will only be fully elucidated when the species and transformation of species in the living system have been measured (ComeUs 1996 Cornelis et al. 1998). Ultimately there will be a need for adequate RMs certified for the trace element species bound to large molecules, such as proteins. 

New developments are, however, needed to make a major step forward in the field of speciation analysis. The first part, isolation and separation of species, may be the easiest one to tackle. For the second part, the measurement of the trace element, a major improvement in sensitivity is needed. As the concentration of the different species lies far below that of the total concentration (species often occur at a mere ng/1 level and below), it looks like existing methods will never be able to cope with the new demands. A new physical principle will have to be explored, away from absorption spectrometry, emission spectrometry, mass spectrometry, and/or more powerful excitation sources than flame, arc or plasma will have to be developed. The goal is to develop routine analytical set-ups with sensitivities that are three to six orders of magnitude lower than achieved hitherto. 

Speciation involves a number of discrete analytical steps comprising the extraction (isolation) of the analytes from a solid sample, preconcentration (to gain sensitivity), and eventually derivatisation (e.g. for ionic compounds), separation and detection. Various problems can occur in any of these steps. The entire analytical procedure should be carefully controlled in such a way that decay of unstable species does not occur. For speciation analysis, there is the risk that the chemical species can convert so that a false distribution is determined. In general, the accuracy of the determinations and the trace-ability of the overall analytical process are insufficiently ensured [539]. 

With the exception of GC-MIP-AES there are no commercial instruments available for speciation analysis of organometallic species. Recently, a prototype automated speciation analyser (ASA) for practical applications was described [544,545], which consists of a P T system (or focused microwave-assisted extraction), multicapillary GC (MC-GC), MIP and plasma emission detection (PED). MCGC-MIP-PED provides short analysis times ([Pg.676]

Mass spectrometry can be specific in certain cases, and would even allow on-line QA in the isotope dilution mode. MS of molecular ions is seldom used in speciation analysis. API-MS allows compound-specific information to be obtained. APCI-MS offers the unique possibility of having an element- and compound-specific detector. A drawback is the limited sensitivity of APCI-MS in the element-specific detection mode. This can be overcome by use of on-line sample enrichment, e.g. SPE-HPLC-MS. The capabilities of ESI-MS for metal speciation have been critically assessed [546], Use of ESI-MS in metal speciation is growing. Houk [547] has emphasised that neither ICP-MS (elemental information) nor ESI-MS (molecular information) alone are adequate for identification of unknown elemental species at trace levels in complex mixtures. Consequently, a plea was made for simultaneous use of these two types of ion source on the same liquid chromatographic effluent. 

For chemical speciation, X-ray absorption spectroscopy is another supreme tool taking advantage of its electronic and structural information power. Also, REMPI-MS is outstanding in its selectivity for molecular species. Radioanalytical methods have also been used for speciation analysis [548]. Microscopical speciation analysis requires SSIMS or LMMS [549]. 

Clay speciation analysis, dominated by the use of short-wave infrared techniques, highlights variations in the clay alteration associated with these deposits. The presence of a key species, such as illite, may be locally significant, but absolute amounts of each clay relative to alteration intensity are typically unattainable from these types of analyses. 

Another intensively studied element in speciation analysis is arsenic. The biological and environmental effects of arsenic species and their transformation pathways have been studied in numerous papers.40- 42 Both arsenite and arsenate accumulate in living tissues because of their affinity for proteins, lipids and other cellular compounds.43 Arsenic species can undergo transformation via... 

Figure 1.12 Species-selective hyphenated techniques for speciation analysis.

H. Matusiewicz and M. Krawczyk, Determination of total antimony and inorganic antimony species by hydride generation in situ trapping flame atomic absorption spectrometry a new way to (ultra)trace speciation analysis, J. Anal. At. Spectrom., 23, 2008, 43-53. 

Li and coworkers [193] reported a hybrid technique for rapid speciation analysis of Hg(I) and MeHg(II) by directly interfacing an NCE to atomic fluorescence spectrometry. Both mercury species were separated as their cysteine complexes within 64 seconds. The precision (RSD, n = 5) of migration time,... 

In both cases the species, forms or phases are defined (a) functionally, (b) operationally, or (c) as specific chemical compounds or oxidation states. This usage is employed in this book but IUPAC has proposed a useful clarification in that definition (1) above is abandoned in favour of speciation analysis and the term spe-ciation is reserved for the concept of a description of the distribution of species. 

Total metal concentrations are often very low in natural systems and in performing speciation analysis it is necessary to measure even lower concentrations on attempting to resolve component species. Therefore, very sensitive methods are needed and there is a high risk of contamination, alteration and/or adsorption losses. The ideal speciation method would be sufficiently sensitive and selective to be used directly on natural water samples, would involve minimal perturbation of the sample, and would furnish an analytical signal directly dependent on the (chemical) reactivity of the element of interest (Buffle, 1981a) (Fig. 8.1). 

Szpunar-Lobinska, J., Witte, C., Lobinska, R. and Adams, EC. (1995) Separation techniques in speciation analysis for organometallic species. Fresenius J. Anal. Chem., 351, 351-377. 

Anodic stripping voltammetry (ASV) is a very sensitive instrumental technique for the measurement of metals in solution. Of particular importance are determinations of reactive or ASV-labile metal concentrations. ASV-labile metal is defined as the fraction of the total metal concentration that is measured under a defined set of ASV and solution conditions. Labilities of metal species in natural water have been related to toxicities. Thus, one objective of speciation analysis carried out by ASV is to find conditions where the ASV-labile fraction is a close approximation to the toxic fraction of a metal. In experimental terms, the ASV-labile metal should be equal to the electroactive fraction of the metal. The latter... 

Attempts at environmental or health protection can yield only dubious results, if any, if they are based on suspect data. Therefore, a rigid quality control program is required for speciation analysis. Species alterations have to be avoided or minimized information on the degree of possible species changes must therefore be elucidated.32 39... 

Performing the chemical speciation analysis on the unaltered specimen with SIMS alleviates this uncertainty. However, the results are fundamentally more difficult to interpret, for certain species that are more ambiguous, and for other species with which the technique cannot be made to work. Each situation is obviously quite different and care must be exercised in choosing a method. 

A rapid and simple MW-assisted digestion method with alkaline solution (TMAH or methanolic KOH solution) was developed for speciation analysis of inorganic Hg and methyl-Hg in biological tissues [41]. Extracts with quantitative recoveries of Hg species after the alkaline dissolution of the sample were directly analyzed by an automated on-line hyphenated system incorporating aqueous HG, cryogenic trapping, GC, and detection by A AS. The proposed method was validated by the analysis of biological CRMs (CRM 463, DORM-1, TORT-1) and one BCR sample from an interlaboratory study (Tuna Fish 2). 

A simple and rapid procedure was developed for the simultaneous determination of methyl-Hg and Hg(II) in Psh CRMs [43], The procedure was based on a rapid MW-assisted solubilization of biomaterial with TMAH, simultaneous quantitative ethylation-extraction of the Hg species into hexane, Bash isothermal separation using minicolumns, and Pnal detection by MIP-AES. The method was validated for speciation analysis for HG using the BCR 463 and 464 Tuna Fish CRMs. 

Speciation analysis, on the other hand, plays a pivotal role in a more realistic assessment of the impact on human health of the intake of potentially toxic elements through the diet (see also Chapters 16-22 in this book). Recent studies on chemical speciation of As in rice showed that the percentage of the inorganic As (III) and As (V) species, i.e., the most toxic ones, range from 11 to 91 percent, a much higher percentage than in other foods [45, 46],... 

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