Speciation analysis total

Today it has become clear that the effect of trace elements in living systems, in food, and in the environment depends on the chemical form in which the element enters the system and the final form in which it is present. The form, or species, clearly governs its biochemical and geochemical behaviour. lUPAC (the International Union for Pure and Applied Chemistry) has recently set guidelines for terms related to chemical speciation of trace elements (Templeton et al. 2000). Speciation, or the analytical activity of measuring the chemical species, is a relatively new scientific field. The procedures usually consist of two consecutive steps (i) the separation of the species, and (2) their measurement An evident handicap in speciation analysis is that the concentration of the individual species is far lower than the total elemental concentration so that an enrichment step is indispensable in many cases. Such a proliferation of steps in analytical procedure not only increases the danger of losses due to incomplete recovery, chemical instability of the species and adsorption to laboratory ware, but may also enhance the risk of contamination from reagents and equipment. 

New developments are, however, needed to make a major step forward in the field of speciation analysis. The first part, isolation and separation of species, may be the easiest one to tackle. For the second part, the measurement of the trace element, a major improvement in sensitivity is needed. As the concentration of the different species lies far below that of the total concentration (species often occur at a mere ng/1 level and below), it looks like existing methods will never be able to cope with the new demands. A new physical principle will have to be explored, away from absorption spectrometry, emission spectrometry, mass spectrometry, and/or more powerful excitation sources than flame, arc or plasma will have to be developed. The goal is to develop routine analytical set-ups with sensitivities that are three to six orders of magnitude lower than achieved hitherto. 

Since the concentrations of the various compounds or oxidation states in which trace elements can occur are always lower than the total content of the analyte, speciation analysis is normally an ultratrace determination in the ng L-1 range for solutions and the ng g 1 range for... 

The aim of this work was to investigate the arsenic mobilization from the tailings material (200 - 500 pg/g As) into the seepage water (up to 3.5 mg/L As) and the process of seepage water effluent forming an immobilized precipitate (up to 8 % As) in the creek. Different analytical methods for the determination of total concentrations and different sequential extraction methods as well as hyphenated techniques for speciation analysis were applied to follow the way of the arsenic in this environment. 

H. Matusiewicz and M. Krawczyk, Determination of total antimony and inorganic antimony species by hydride generation in situ trapping flame atomic absorption spectrometry a new way to (ultra)trace speciation analysis, J. Anal. At. Spectrom., 23, 2008, 43-53. 

Total metal concentrations are often very low in natural systems and in performing speciation analysis it is necessary to measure even lower concentrations on attempting to resolve component species. Therefore, very sensitive methods are needed and there is a high risk of contamination, alteration and/or adsorption losses. The ideal speciation method would be sufficiently sensitive and selective to be used directly on natural water samples, would involve minimal perturbation of the sample, and would furnish an analytical signal directly dependent on the (chemical) reactivity of the element of interest (Buffle, 1981a) (Fig. 8.1). 

Anodic stripping voltammetry (ASV) is a very sensitive instrumental technique for the measurement of metals in solution. Of particular importance are determinations of reactive or ASV-labile metal concentrations. ASV-labile metal is defined as the fraction of the total metal concentration that is measured under a defined set of ASV and solution conditions. Labilities of metal species in natural water have been related to toxicities. Thus, one objective of speciation analysis carried out by ASV is to find conditions where the ASV-labile fraction is a close approximation to the toxic fraction of a metal. In experimental terms, the ASV-labile metal should be equal to the electroactive fraction of the metal. The latter... 

Speciation analysis comes into its own mainly in environmental, nutritional, and biomedical research. The sample matrices are generally highly complex and the requirements for reliable (trace) element determinations are stringent (even for total amounts). The most important challenges in this context involve... 

The advantage of the selective adsorption of a particular element oxidation state has been exploited for on-line element preconcentration and speciation analysis of Cr by FAAS. Cespon Romero et al. [21] described an FIA system employing a minicolumn made of a chelating resin containing poly(aminopho-sphonic) acid groups, able to selectively retain Cr(III) ions. An FIA manifold was employed for efficient preconcentration and subsequent elution of Cr(III) with a small volume of 0.5 M HC1. The original sample was also treated with ascorbic acid to reduce Cr(VI) to Cr(III) and total Cr is determined as Cr(III) after appropriate retention and elution. Eluates are introduced into an N20-acetylene flame connected to the column outlet. The concentration of Cr (VI) is obtained by difference. Employing a sample volume of 6.6 mL, LoD for total Cr is 0.2 pg l-1. A study of FI operational variables, interferences, and precision is reported for the analysis of tap, mineral, and river waters. 

ET-AAS with graphite furnace tubes constituted the analytical support for the speciation analysis of Al and the concomitant determination of Al (III) in tea infusions, as described by Alberti and coworkers [141], Lvov platforms incorporated into the graphite furnace atomizers enabled the authors to attain an LoD of 2 xg l-1 Al. The determination was not impaired by the relatively high solid contents. Adsorption of Al on ion Chelex-100 resin was employed to estimate the free metal content and the concentration and stability constants of complexed Al species. The metal is reported to be present in total concentrations from 0.09 to 0.26 mM, but mainly linked to strong complexes. Strong complexation is demonstrated by the inability of Chelex-100 to dissociate the complexes. These results are considered by the authors as an explanation of the low toxicity of the Al associated with tea infusions. The concentration of free Al was found to be very low (at the nM level). No structural or chemical information about the ligands was obtained from the method. 

Se Speciation in Plants The presence of a number of volatile Se species was reported in edible allium plants such as garlic by GC-AES [79]. Selenomethionine, Se-methylselenocysteine, and y-glutamyl-Se-methyl-L-seleno cysteine were identibed in garlic and onion by HPLC-ICP-MS and ES-MS/MS [80]. Selenomethionine is the primary species found in all types of nuts (19D25 percent of the total Se) [30], sunBower [81], and mushrooms [36, 37], The distribution of Se among different fractions (lipid extract, low molecular weight, and protein fractions) of nuts and speciation analysis was studied [30]. Selenium was not detected in any of the lipid extracts obtained from the different types of nuts [30], Results obtained for Brazil nuts by SEC with on-line ICP-MS detection showed that approximately 12 percent of total Se was weakly bound to proteins [30],... 

V. Diaz Huerta, L. Hinojosa Reyes, J. M. Marchante-Gay n, M. L. Fernandez Sanchez, A. Sanz-Medel, Total determination and quantitative speciation analysis of selenium in yeast and wheat Bour by isotope dilution analysis ICP MS, J. Anal. Atom. Spectrom., 10 (2003), 1243D1247. 

In brief, today the scientific community worldwide recognizes the need to carry out speciation analysis, not just total determinations, of both essential and potentially toxic elements in milk. 

These analytical problems regarding total element determination in human milk are magnified in milk speciation analysis as this requires a series of carefully planned steps of which chemical and/or physical pretreatments of the sample are almost always mandatory. In this context, both sampling and sample preparation... 

On the basis of the experience accrued so far, the extraction efficiency can be affected by both the nature of the sample under test and the As species actually present in the sample. The lipid content of the sample and the presence of As species with hydrophobic residues play a key role in this context. As a consequence, it may be useful to remove or partition lipids with an organic solvent prior to the methanol-water extraction in order to increase the extraction efficiency. This approach is also viable to prevent emulsification of methanol and lipids, which could otherwise significantly reduce the extraction efficiency [26]. Thus, sample preparation prior to As speciation usually starts with the chloroform-methanol extraction, followed by centrifugation of the sample solution to remove solid particles. Subsequently, after the addition of methanol and water, the supernatant is separated in a funnel. The amount of As remaining in the organic phase is usually quantified as total As by wet digestion after solvent evaporation. Obviously, this entails the loss of all speciation information related to the lipid-soluble As species [2]. Speciation analysis is finally carried out on the methanol-water phase, usually after solvent evaporation (see Table 19.2). 

Enhancing the Se levels in crops can be achieved by adding organic amendments (manure of Se-supplemented farmed animals) or inorganic Se to mineral fertilizers [116, 117]. The use of sodium selenate-enriched fertilizers in Finland resulted in increased Se levels in different foods and, consequently, the average serum Se in the population improved over the period 1984 D1988. ICP-MS was used to study the feasibility of wheat enrichment by selenate addition to soil fertilizers [118]. AE-HPLC-ICP-MS was optimized for the separation of selenite, selenate, selenocysteine, and selenomethionine. Total Se determination and speciation analysis were performed in water extracts and in enzymatic digests of wheat samples. It was shown that a major part of the selenate taken up by cereals was converted to selenomethionine. 

In past years, on line chromatographic coupling techniques such as HPLC and CE coupled to ICP-MS with the isotope dilution technique have been used for element quantification in speciation analysis. An interesting application of the isotope dilution technique in medical research was proposed recently by Prange and co-workers, who added highly enriched " S, Cu, Zn and Cd spikes to the interface of the CE-ICP-MS system. The authors separated isoforms of metallothionein (e.g., of rabbit liver) by capillary electrophoresis and quantified S, Cd, Cu and Zn concentrations in isoforms by ICP-SFMS using the isotope dilution technique. A new selenized yeast reference material (SELM-1) for methionine, selenomethionine (SeMet) and total selenium content has also certified by an intercomparison exercise. ... 

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