New concepts in speciation analysis

Abstract

Speciation analysis is a term used to describe the process whereby the analyte is characterised subject to a set of defined criteria, typically yielding information about:-the chemical form of the analyte that is functionally important (e.g. ligands on an organometallic species or oxidation state) -the exact structural and chemical form of the analyte (e.g. NMR-derived structure) -the nature of the chemical species as determined from an operational point of view, dependent on the method of sample preparation or analysis used (e.g. metals extractable by acetic acid or other solvent).The International Union of Pure and Applied Chemistry (IUPAC) has defined speciation as "the specific form of a chemical element defined according to its molecular, complex, electronic or nuclear structure" [1]. Hence, speciation analysis can be considered to be the identification and quantification of the different chemical and physical forms of an element existing in a sample. The chemical form of an element will determine its toxicity, stability and transport, so this measurement is a very important factor in the wider definition of speciation. In chemical analysis, the quantitative and qualitative determination of specific chemical species is long established, especially for non-metallic species (e.g. the different forms of nitrogen: NO 3 -, NO 2 -, NH 4 + and NH 3 ). However, much of the recent effort in analytical chemistry has focused on the speciation of metals [2, 3] because of their functionality as part of biologically important enzymes and co-factors, and their toxic effects in the environment. Likewise, a large body of research exists on the partitioning of compounds between different states or phases, particularly with respect to the fate of environmental pollutants and nutrients [4].The awareness of the need for speciation techniques has gradually arisen as various pollution and poisoning incidents have been investigated. The residents of Minamata Bay in Japan suffered acute and chronic mercury poisoning, with brain damage to new-born infants, as a result of a release of inorganic mercury into the Bay, followed by methylation to methylmercury and its subsequent bioaccumulation in fish, due to its lipophilic nature [5]. A population crash, combined with changes in shell shape and meat content, decimated the oyster farming industry of Arcachon Bay in France and was traced to the use of tributyltin (TBT) as an anti-fouling agent [6]. In contrast, inorganic tin is a relatively innocuous compound.More recently, the concept of speciation analysis has found application in a wider range of fields, so a broader definition which encompasses this is appropriate. It is convenient to frame the question "What do I want to know about the analyte?" and define speciation analysis in terms of the type of information required, namely:-how much analyte is present in total? -how much is available? -what is its chemical form/structure? -how is it distributed? -how stable is it?When considered in these terms, the definition of speciation inclu...

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