Speciation

[Anonymous]

Speciation in chemistry is defined as the distribution of an element amongst chemical species in a system, relating to isotopic composition, electronic or oxidation state, and/or complex or molecular structure. New terms have been proposed by INFOODS for both elemental oxidation states, such as Fe(+2) and Fe(+3), and for specific isotopes. e.g. strontium-90.  Both oxidation-state and isotopic speciation will involve thesaurus codes based on chemical element symbols that are extended with an indication of the specific form being reported and both will be covered by this forum topic.

INFOODS have proposed tagnames that append the isotope number to the element symbol and included CS137, ID131, PU239 and SR90 in the 2008 additions.  It is proposed to add these terms to the EuroFIR Component Thesaurus.

Oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound.  It is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic, so that the sum for all atoms of a neutral molecule is zero.  However, in many cases an atom is not fully ionic and the amounts present in a food for a given oxidation state and the corresponding ion will differ.  Thus Fe(+2) (the ferrous oxidation state) is different from Fe(2+) (the ferrous ion) and the corresponding thesaurus terms must be used only to represent the form defined.

The INFOODS 2008 and 2010 additions proposed oxidation-state tagnames that included the plus sign, e.g. FE2+ for Fe(+2), but it was recently decided to retain the restrictions on characters to those in XML tags, barring use of the plus sign.  As an alternative, the use of P (for plus/positive) and N (for negative) has been suggested, separated from the number by the underscore character, e.g. FE2_P for Fe(+2).  However, as the underscore is usually used to separate distinct parts of the code (see, for example, Mixtures and condensation products), this usage within the representation of oxidation number may be confusing.  A better option might be to use the underscore to separate the representation of oxidation from the atomic symbol, e.g. as FE_P2 (for ferrous oxidation state of iron) .  This has the further advantage that it uses the conventional order of characters for oxidation state, leaving the alternative order of FE_2P available to represent Fe2+, the ferrous ion, if this is required in the future.

Any comments on these proposals for harmonising the representation of isotopes (e.g. SR90) and oxidation states (e.g. FE_P2) in EuroFIR component identifiers and INFOODS tagnames would be much appreciated.

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