Atomic spectrometry update. Elemental speciation

This is the third Atomic Spectrometry Update (ASU) to focus specifically on developments in elemental speciation. The International Union for Pure and Applied Chemistry (IUPAC) have evaluated speciation and provided a definition as follows: speciation analysis is the analytical activity of identifying and/or measuring the quantities of one or more individual chemical species in a sample; the chemical species are specific forms of an element defined as to isotopic composition, electronic or oxidation state, and/or complex or molecular structure; the speciation of an element is the distribution of an element amongst defined chemical species in a system. Within this review period an IUPAC Technical Report describing the guidelines for the terminology and critical evaluation of analytical chemistry approaches related to the area of metallomics, has been published. The working group define the metallome as the entirety of metal-and metalloid species present in a biological system, defined as to their identity and/or quantity. Metallomics itself is defined as the study of the metallome, interactions and functional connections of metal ions and other metal species with gene, proteins, metabolites and other biomolecules in biological systems. This review will therefore deal with all aspects of the analytical speciation methods developed for: the determination of oxidation states; organometallic compounds; coordination compounds; metal and heteroatom-containing biomolecules, including metalloproteins, proteins, peptides and amino acids; and the use of metal-tagging to facilitate detection via atomic spectrometry. The review will not specifically deal with operationally defined speciation, but will highlight other reviews which cover the work in this area. As with all ASU reviews, the coverage of the topic is confined to those methods that incorporate atomic spectrometry as the measurement technique. However, in the spirit of meeting the needs of the subject, we will incorporate material that is not strictly atomic spectrometry. For the most part, such procedures are those in which some form of molecular MS is the measurement technique. There is a growing role for this kind of MS either as the sole instrumental technique or in parallel with an elemental detector. As the contents of this Update show, there is considerable activity in the development and application of methods of elemental speciation analysis, which for some elements and combinations of techniques is a mature field as shown by the extent to which relevant topics have been the subject of review articles.