Trace elements, in biological systems

Trace elements, in biological systems. 941-953 Transactinide elements. 599-607, 613-617... 

Iron enjoys a unique position as an essential trace element in biological systems. By virtue of its role in electron transfer it is generally present in higher concentration than the other trace elements. At the same time its extreme insolubility at physiological pH and the myriad of reaction... 

The substoichiometric principle is also applied for determination of trace elements in biological systems. Some examples are listed in Table 19.1. The detection limits are usually <1 mg/1, in some cases (e.g. (QH6)2Hg) <10 nig/1. 

The chemical speciation study of trace elements in life sciences has been paid more and more attention in recent years, mainly because it can provide more significant information on the pathway, distribution, accumulation, excretion, and functions of trace elements in biological systems of interest than the traditional bulk composition study. Almost all speciation techniques consist of two steps. The first step involves the separation of species from the sample followed by the second step of element specific detection. The so-called molecular neutron activation analysis (MoNAA) or speciation neutron activation analysis (SNAA) is, in fact, a combination of conventional NAA with physical, chemical, or biological separation procedures in order to meet the ever-increasing need for chemical species study. 

The information on the chemical speciation of trace elements in biological systems is much needed to evaluate their biological significance. Although a number of analytical techniques based on atomic behavior are available for the analysis of chemical speciation of trace elements, neutron activation analysis, as a nuclear analytical technique, can be successfully used in chemical speciation studies, after appropriate fractionation steps. Table 2.5 lists some typical applications of NAA in chemical speciation analysis of metalloproteins. The main advantages of NAA are of its high sensitivity and the absence of matrix effects inherited from the conventional neutron activation analysis. It can, therefore, be used to analyze the chemical species of trace elements in very small samples or complicated matrices, which is often impossible for non-nuclear techniques. 

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