Elemental Speciation in Biological Samples

Miniaturization of HPLC-ICP-MS is an important issue in bioanalytical chemistry when small amounts of sample (e.g., single cells) need to be investigated.33 ICP-MS (with an octopole collision cell) in combination with nano-HPLC (75 pun column) was optimized for the detection of selenopeptides in a selenium-yeast protein digest after 100-fold preconcentration on a C18 capillary precolumn (300 (im column for salt removal and cleanup).34 Under identical separation and preconcentration conditions, electrospray MS/MS (using Nanospray qQqToF-MS - QSTAR from Applied 

Simultaneous speciation of inorganic selenium and tellurium in water samples by ICP-MS was performed after selective solid phase extraction (SPE), as discussed by Yu et al 9 Under acidic conditions Se (IV) and (TV) complexes with ammonium pyrrolidine dithiocarbamate were formed. The detection limits for Se and species in water samples were found to be 7ngl 1 and 3 ng 1 1, respectively. 

Another intensively studied element in speciation analysis is arsenic. The biological and environmental effects of arsenic species and their transformation pathways have been studied in numerous papers.40- 42 Both arsenite and arsenate accumulate in living tissues because of their affinity for proteins, lipids and other cellular compounds.43 Arsenic species can undergo transformation via 

An interesting approach was proposed in Lobinski s group for the analysis of non-covalent Ni species in biological samples.49 The Ni species in aqueous plant tissue extracts were quantitative determined by SEC-ICP-MS in combination with ESI-ToFMS/MS after purification of Ni species by hydrophilic interaction HPLC (HILIC).49 

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. 

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

Herein, reports on simultaneous multi-elemental speciation in biological samples are summarized in Table 1.6. More examples focusing on specific techniques are included in the subsequent chapters, respectively. 

Sanz-Medel a. and Bianco-Gonzalez E. (2002) Chiral trace-element speciation in biological samples present importance and applications to speciation for seleno-amino acids, Trends Anal. Chem. 21 709-716. 

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. 

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. 

The distribution of an element in biological samples collected from an ecosystem can be equally complex. In plants, for example, the distribution of minor elements or particular species is not uniform throughout the whole organism, i.e. leaf material values differ from those derived from ribs, stems, roots and fruit. For speciation, sub-sectioning of the semi-rigid matrix may thus have to precede isolation of the component of interest. 

The unique aspects of speciation procedures arise from the additional specification that the procedure adopted should not disturb existing equilibrium conditions. The choice of procedure is further restricted by the fact that the total concentration of element present in a sample (e.g. Cu, Pb, Cd, Zn in water samples) is often near the detection limits of many standard analytical techniques, and modified or refined techniques are required to handle the even lower levels present in isolated sub-categories. In biological matrices, the concentrations of inorganic and organo-metallic compounds present can range from 10 3 to 10 12 mol dm 3, and at the lower levels even the determination of total element content can be greatly in error, if suitable correction is not made for interference effects which can arise from the nature of the sample. 

A. Sanz-Medel, E. Blanco-Gonzalez, Chiral speciation of trace elements approaches to the speciation of selenoaminoacid enantiomers in biological samples, J. Anal. Atom. Spectrom., 16 (2001), 957-963. 

Another factor of importance in the choice of a fractionation technique is the sensitivity of the detection technique because the total concentration of some trace elements in biological samples lie at the limit of detection of most conventional techniques. Therefore fractionation methods in which the species are extensively diluted can only be used for these elements when it is possible to concentrate the fractions afterwards. Current technology enables analyte concentrations of about 1 fig/L to be determined in biological matrices. However, at these levels special precautions have to be taken to avoid contamination from external sources, and it is difficult to establish the accuracy of the determination. At present the speciation of metals or metalloids present at total levels less than 100 fig/L can only be undertaken with time-consuming and tedious methods which increase the probability of altering the metal-ligand interaction. 

Chemical speciation of the elements in biological samples and systems... 

Figure 3.10 Scheme of the workflow for trace element speciation analysis in biological samples with electrophoresis and SRXRF. 

This section will introduce the application of Mossbauer spectroscopy for the study of elemental speciation in environmental and biological samples. The... 

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. 

EXuring storage there are changes in the sample that may have some consequence for the speciation of an element. First, the complex three-dimensional structure of most biological molecules may be destroyed. This may lead to the loss of enzymatic activity, and in some cases the associated element may be lost. Second, the natural proteolysis and/or autolysis reactions could result in the breakdown of the molecules, and as a con uence the results of the speciation experiments may indicate that the element is associated with only a fragment of the original molecule. Indeed,... 

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