The term speciation

In this context the term speciation may be defined as either... 

The term speciation is used for a wide variety of analyses, ranging from the determination of well-defined species , e.g. oxidation states of elements or... 

The term speciation , according to Bernhard et al. (1986a), encompasses three aspects (1) the actual distribution among molecular level entities in a given matrix, (2) the processes responsible for an observable distribution (species distribution), and (3) the analytical methods used (species analysis). Aspects (1) and (3) are compatible with the definition given by Ure (1990) and presented in Chapter 1. The second aspect, (2) above, is now seldom used in chemistry and... 

In general, there are at least three approaches to the use of the term speciation analytics in the analytical context ... 

According to International Union of Pure and Applied Chemistry (IUPAC), the terms speciation and chemical species should be reserved for the forms of an element defined as to isotopic composition, electronic or oxidation state and/or complex or molecular structure (Templeton el al, 2000). This classical definition, appropriate to speciation in solution samples, would exclude most speciation studies on solid materials, such as soils and sediments, more properly defined as fractionation studies. The terminology used in this chapter is based on the broader definition of speciation given by Ure and Davidson (2002), which encompass the IUPAC s narrow definition and includes the selective extraction and fractionation techniques of solid samples. 

The term speciation is used to describe any analytical procedure in which the amounts of an element in discrete chemical forms are determined, as opposed to the total amount of an element in the sample. For example, it may be of interest to determine the amounts of Cr3 + and Cr042 in environmental samples, if the two ionic species have different toxicities, rather than the total amount of chromium. In this instance ion exchange may be used to separate the cationic and anionic species.23 Sometimes all the species to be determined may be either cationic or anionic, as in the case of the determination of Fe2+ and Fe3+ or S2, S032-, and S042-. Sometimes inorganic and organically bound forms may be determined, as in the case of arsenic species in natural waters.24 Where flame spectrometric determination has been employed in speciation studies of this type, selected key references may be found in the element-by-element section of Chapter 6. 

In soil research, the term speciation is often applied to operationally defined fractionation of heavy metals into five or more components.25 Typically, water soluble, exchangeable, organically bound (which includes what is in biomass), amorphous oxide bound, crystalline oxide bound, and residual fractions are measured.26 Sometimes residual fractions are further subdivided according to particle size distributions to give amounts in sand, silt, and clay fractions. Similar fractionation procedures are often applied to aquatic sediments.27 In arid regions, often the calcium carbonate bound fractions of heavy metals are also measured.28 Because of the constraints of detection limits, generally only cadmium, copper, iron, manganese, and zinc are usually monitored by flame spectrometry in such heavy metal speciation studies.28... 

The term speciation is used to describe the reactions that take place when an electrolyte is dissolved in water. Water dissociates, sour gases hydrolyze, some ions dissociate, and other ions associate until thermodynamic equilibrium is attained. The liquid phase of the ternary H2O-NH3-CO2 system contains at least the following nine species HjO, NH3(aq), COjiaq), H", OH, NH4, HCOj, COj , and NHjCOO. (aq) indicates that the species is in aqueous solution to avoid ambiguity. In order to adequately model this system, interaction parameters for the interaction between each pair of species need to be determined thus, speciation calculations are performed simultaneously with the parameter estimation, and the calculated amount of each species is compared with experimental data. Some models also require ternary parameters and consequently an additional amount of data to determine these parameters. 

The general experience that the environmental behavior and toxicity of an element can only be understood in terms of its actual molecular form led to the introduction of the term speciation", which is used in a vague manner both for the operational procedure for determining typical metal species in environmental samples and for describing the distribution and transformation of such species in various media (Leppard,... 

Speciation of an element The term speciation is used to indicate the distribution of defined chemical species in a particular sample or matrix. This means that an element existing in different forms must be regarded as representing different species. Shortened versions of the definitions given above are listed in Table 3.1. 

The term speciation refers to the determination of the chemical form of metals and metalloids and according to lUPAC it is the process yielding evidence of the atomic or molecular form and oxidation state of an analyte. Included in this definition are the organometallic compounds and those of N, P, S and Si. The determination of organic substances is not referred to. 

A contaminant can occur in many different forms in an environmental compartment, each of them having different mobility, transfer coefficients to and between living matter, and even toxicity. This variety of existing forms for a given element is termed chemical speciation, defined as the distribution of one or more elements between all its possible species (distinct chemical entities) in a given system. It should be noted that the term speciation is also used in another context to describe all the experimental methods applied to investigate the above discussed species distribution. 

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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