Speciation of metals and metalloids in biological systems

The reasons for studying the distribution of metal- and metalloid-containing species in biological systems include  

In this chapter, the factors influencing the distribution of metal- and metalloid-containing species are discussed, and more recent developments in understanding the behaviour of antimony, arsenic, selenium and tin in biological systems are reviewed. 

Bioavailable metals and metalloid species are either adsorbed or incorporated into the structure of proteins, lipids, nucleic acids, amino acids, sugars, vitamins and hormones to form complexes of varying degrees of thermodynamic stability and reactivity. These complexes could be classified as either metal-proteins or metalloproteins on the basis of their stability during isolation and purification (Vallee and Coleman, 1964). Whereas metal-proteins are relatively labile and the metal is easily lost during dialysis, metalloproteins are stable and inert. 

In general, species containing transition metals and metalloids such as As, Sb, Se and Sn are thermodynamically more stable than those of the alkali and alkaline earth metals. Transition metals and metalloids form an integral part and are linked to the organic constituents by covalent bonds. In contrast alkali and alkaline earth metals are attached loosely by predominantly ionic bonds. Readers interested in the fundamentals of metal-protein interactions are referred to books 

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The number of analytical methods developed for the study of the distribution of metal- and metalloid-containing species in the last decade has been impressive. However, a majority of these are as yet to be applied to real biological materials. With the greater appreciation of the pre- and post-sampling factors that influence chemical speciation, and the development of appropriate quality control materials the results of these studies will become more reliable. Consequently, the use of chemical speciation data will become indispensable to accurate environmental impact assessment, and to our understanding of the roles that metals and metalloids play in biological systems. 

Wine is a very complex matrix and the accurate, selective determination of species constitutes a challenge for analytical chemists. Furthermore, the speciation analysis of metals bound to biological ligands is a subject of increasing interest since complexation may reduce their toxicity and bioavailability. There is a limited number of studies concerning the speciation analysis of metals or metalloids in wines. Arsenite, arsenate, MMA, and DMA were separated in less than 10 min by means of an anion-exchange column [88], Arsenic species detection was accomplished by the direct coupling of the column effluent to an HG system and AFS was used for detection. LoDs in white wine were 0.16, 0.33, 0.32, and 0.57 ng ml-1 for As(III), DMA, MMA, and As(V), respectively. In real samples... 

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