Trace Elements, Chemical Species and Speciation Analysis

1 Trace Elements, Chemical Species and Speciation Analysis 

The biological eflect of an element is not only dependent on the total concentration, but also highly related to its chemical forms present in biological systems, e.g. the oxidation state, the nature of the ligands or even the molecular structure. Dramatic examples are chromium, tin and mercury, to name just a few. Cr(VI) ions are considered far more toxic than Cr(III). Although the inorganic forms of tin and mercury are less toxic or even do not show toxic 

Nowadays, there is increasing awareness of the importance of the chemical form in which an element is present in biological systems. More and more chemical speciation information on a given element is demanded in most fields of research. In fact, many environmental, toxicological, pharmacological, nutritional, and biological issues today require reliable information on the actual chemical species present, rather than total element concentrations as usually provided by atomic techniques in routine laboratories. In recent years, trace element speciation has become a worldwide trend in current analytical chemistry. Often these different chemical forms of a particular element or its compounds are referred to as species . 

Although the concept of speciation is now widely appreciated in many fields, these terms have been used in a number of different ways and created confusion. In a report on the 1984 workshop The Importance of Chemical Speciation in Environmental Processes , Bernhard et al. pointed out that the usage of speciation varies among different fields ranging from evolutionary changes to distinctions based on chemical state. The term has been used in no fewer than four different ways including the reaction specificity, transformation of species, the distribution of species, or the analytical activity to determine the concentrations of species. They concluded that authors should either avoid the term altogether or clearly define it. 

In an attempt to end the confusion that existed regarding the usage of the term speciation, the International Union of Pure and Applied Chemistry (lUPAC), (three lUPAC Divisions represented by the Commission on Microchemical Techniques and Trace Analysis, the Commission on Fundamental Environmental Chemistry, and the Commission on Toxicology) provided lUPAC Recommendations in 2000 in an attempt to define what is a chemical species, what is speciation and what is speciation analysis. It was agreed that straightforward, standard terminology is important for interdisciplinary 

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