Biology elemental speciation

It is not possible to prescribe specific pretreatment procedures here because these can only be decided upon when the system and the purpose of the experiments has been properly defined. However, a wealth of information exist in various biochemical reference books on how to isolate various biological compounds. The recommended techniques and methods could be used as part of the trace element speciation protocol often after slight modification, taking into consideration the following points First, the trace element blank levels have to be low, less than 10% of the total concentration in the sample. Second, the regents used should not interfere with subsequent analytical determinations. Third, the experimental conditions should not deviate markedly from those found in vivo, especially the pH and ionic strength of the medium. 

Szpunar, Lobinski el al. have reported on several hyphenated techniques (especially CE-ICP-MS and HPLC-ICP-MS) for elemental speciation in biological systems,51-54 describing e.g. the quasi-simultaneous determination of more than 30 selenopeptides using HPLC-ICP-MS. 

In the last few years, we have seen the application of isotope dilution methodologies to some new analytical fields. One of these is elemental speciation , where the aim is to determine individual chemical species in which an element is distributed in a given sample. IDMS has also proved its usefulness in element speciation, in which either species-specific or species-unspecific spikes can be used. For example, species-specific IDMS is nowadays used in several laboratories as an effective tool to validate analytical procedures for speciation and to investigate and document eventual interconversion between species. In addition, the study of induced variations in the isotopic composition of a target element can also provide insight into various (bio)chemical and physical processes isotopic analysis is, therefore, also of increasing importance in biological studies. 

J. Szpunar, R. Lobinski and A. Prange, Hyphenated techniques for elemental speciation in biological systems, Appl. Spectrosc., 57, 2003, 102A-112A. 

The various strategies and methodologies for element speciation are discussed in depth in the first part of this book, Techniques for Speciation . This chapter deals with current trends and recent developments in techniques and with recent examples of their application in different compartments of the environment. It also presents recent studies on the speciation of a group of biologically important elements. 

Elemental speciation is the identification and quantification of the chemical form of an element. Traditional analytical techniques for trace elemental analysis have focused on determining the concentration of a particular element within a sample. However, knowledge of total element concentration may not provide sufficient information to determine toxicity since the toxicity of many elements is dependent upon their chemical forms. The oxidation state of the element as well as the organic substituents attached to it may have a dramatic effect on the biological properties observed. As a result, researchers have endeavored to develop new and better analytical techniques that are capable of performing elemental speciation. 

SPME is an emerging analytical tool for elemental speciation in biological samples... 

Human milk can be considered the optimal food for infants. It contains all the macronutrients and micronutrients necessary for the correct development of the newborn and at the adequate levels. When infants are not breast-fed, or breastfeeding is discontinued very early, formula milks are used instead. Therefore, it is important to evaluate the capacity of formulas to deliver satisfactory quantities of minerals and trace elements that can be bioavailable to the children in order to cover their biological needs. This fact explains the need to perform trace elements speciation analysis in formula milk. Thus, the speciation results obtained in formulas and published so far are critically evaluated here and compared with those obtained in human milk. 

A case that joins the problems of trace organic and inorganic analysis is speciation analysis, whose importance has been appreciated in the last few decades. Speciation studies became the center of interest of inorganic analysts when they demonstrated that various derivatives of the same element can exert fully different chemical and biological activities. Speciation analysis requires determination, at the trace level, of organic compounds of metals and nonmetals in various environmental objects. These compounds can be fully of anthropogenic origin... 

Element speciation in biological materials is a difficult analytical task. The challenge is to identify and/or quantify very low concentrations of few to several target species (concentration values far below the total element content) in a complex chemical matrix. Additional difficulties include similar physicochemical properties exhibited by the species of one element and their chemical lability. Very often, not all element forms in the sample are known and, finally, the list of certified reference materials (CRMs) for speciation analysis is still limited. " The two most important features of an analytical tool suitable for speciation analysis are excellent selectivity and high sensitivity. Special care should be paid to preserve the natural composition and distribution of species in the sample during the entire procedure. 

European policies. With the development of the Single Market the exchange of goods and services required agreement on chemical, biological and physical measurements between trade partners, and research demands arose for a wide variety of sectors. Most importantly in the field of environmental analysis, the first CRMs for element speciation and fractionation for metal mobility assessment were issued. 

Smies, M. (1983) Biological aspects of trace element speciation in the aquatic environment. In Trace Element Speciation in Surface Waters and its Ecological Implications, ed. G.G. Leppard, pp. 177-193. New York Plenum Press. 

Some of the difficulties in the unbiased determination of certain trace elements in biological materials may be due to problems of speciation. The range of complex organo-metallic species that can be found in nature is very wide (Frausto da Silva and Williams, 1991). In carrying out an analysis for a particular element in any type of biological fluid or tissues, major assumptions are made concerning the precise chemical composition of element species present. Different analytical techniques will have different sensitivities towards particular element species. Much of the early understanding of the special analytical problems posed by element speciation comes from studies of arsenic (Buchet et al., 1980 Buchet et al., 1981) and mercury (Clarkson, 1983). Problems with other metals remain to be resolved and may require considerable analytical sophistication such as in the analysis of chromium speciation (Urasa and Nam, 1989). 

Last but not least, there will surely develop a great need in future for reference materials that have been certified with respect to specific chemical species. This will be a great challenge for both producers and users of biological reference materials. In order to meet this challenge in addition to the few already existing materials projects have been implemented to arrive at a variety of reference materials for element speciation purposes (e.g. Quevauviller et al., 1993). 

Elemental speciation is becoming more and more important, since the environmental toxicity and biological importance of many elements depend on their oxidation states and different chemical forms. It is accepted today that the most reliable approaches for speciation are tandem techniques, such as hybrid analytical methods involving interfeced chromatography/atomic emission spectrometry (AES) or chromatography/inductively coupled plasma-mass spectrometry (ICP-MS). The low level det ion capability of ICP-MS makes it especially attractive as an element-specific chromatographic detector in chromatography. 

In recent years, many analytical strategies for elemental speciation analysis, particularly in (bio)medi-cal speciation, make use of LC-atomic detector hybrid techniques. Most frequently studied elements include As, Pb, Cd, Sn, Hg, Se, Cr, and A1 both in biological and environmental samples. The capability for multielemental detection of ICP-MS can be most useful in such analysis. An illustrative example of multielement trace-element speciation is metal-lothionein proteins (MT) from rabbit liver by LC-ICP-MS. Comparative profiles for Cd, Zn, Cu, and S obtained for MTs from rabbit liver, using a fast protein liquid chromatography (FPLC) column coupled to ICP-MS are shown in Figure 7, using molecular and specific detectors. 

Cornelius R and De Kimpe J (1994) Elemental speciation in biological fluids - invited lecture. Journal of Analytical Atomic Spectrometry 9 945-950. 

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