Determination of Element Species

Heumann kg, Gallus SM, Radlinger G, and Vogl J (1998) Accurate determination of element species by on-line coupling of chromatographic systems with ICP-MS using isotope dilution technique. Spectrochim Acta 53B z73-287. 

In the present context, we shall restrict our discussion of the determination of elemental species to OT compounds and other organic compounds of group IV elements (Pb and Ge) and Se, since the speciation of other elements is covered in Chapter 7. 

Prange, A., Schaumloffel, D. Determination of element species at trace levels using capillary electrophoresis-inductively coupled plasma sector field mass spectrometry. J. Anal. Atom. Spectrom. 14, 1329-1332 (1999)... 

Determination of Element Species The determination of total element concentrations of PGM in various matrices is sufficient for a first understanding, but a more differentiated analysis is often necessary, in particular with regard to questions concerning bioavaUability, toxicology, pharmacological activity, and pharmacokinetics. The required determination of bonding types and/or bonding partners of the PGM (speci-ation) in environmental samples is rather difficult due to the often very small analyte masses of these elements that usually show intrinsically low natural concentrations. Moreover, the concentrations are further decreased by the limited sample amounts applicable for the separation procedure and the separation into different fractions. Therefore, despite the impressively low LODs of modem analytical methods, the speciation of PGM still often reaches the current analytical limits. 

Not suitable for the determination of elemental species or oxidation states. 

Roltmann, L., and Heumann, K. G. (1994). Development of an on-line isotope dilution technique with HPLC/ICP-MS for the accurate determination of elemental species. Fresenius J.Anal. Chem. 350(4/5), 221. 

Completion of the analysis. The technique of solvent extraction permits the separation and often the pre-concentration of a particular element or substance (or of a group of elements or substances). Following this separation procedure, the final step of the analysis involves the quantitative determination of the species of interest by an appropriate technique. 

Yamamoto et al. [33] applied this technique to the determination of arsenic (III), arsenic (V), antimony (III), and antimony (V) in Hiroshima Bay Water. These workers used a HGA-A spectrometric method with hydrogen-nitrogen flame using sodium borohydride solution as a reductant. For the determination of arsenic (III) and antimony (III) most of the elements, other than silver (I), copper (II), tin (II), selenium (IV), and tellurium (IV), do not interfere in at least 30 000-fold excess with respect to arsenic (III) or antimony (III). This method was applied to the determination of these species in sea water and it was found that a sample size of only 100 ml is enough to determine them with a precision of 1.5-2.5%. Analytical results for surface sea water of Hiroshima Bay were 0.72 xg/l, 0.27 xg/l, and 0.22 xg/l, for arsenic (total), arsenic (III), and antimony (total), respectively, but antimony (III) was not detected. The effect of acidification on storage was also examined. 

This is a powerful method for the determination of the species of elements present in a specific environment. For example, it has been used to determine the arsenic species present in particular environmental conditions [16]. 

The speciation or determination of the chemical nature of an element involves two major processes separation of mixtures and identification of their components. In some cases, adequate identification of the nature of chemical species may be obtained from separation data alone, whereas complete quantitative determination of molecular species requires an initial separation followed by purification of individual compounds. 

In common with other solid materials the determination of element speciation in soils presents a number of difficulties. Firstly, direct determination of speciation in the solid material, without prior separation of the species from the solid matrix, is generally limited to major component elements since few of the direct techniques available are sensitive enough for trace element studies. Resort to separation or extraction of element species presents the usual problem of maintaining the speciation unchanged during the extraction or separation procedure. Despite these difficulties, speciation studies related to nutrient element availability to crops have been a major topic in soil science for more than half a century, uncategorised, however, as speciation until the relatively recent adoption of this terminology. 

Lintchinger, J., Koch, I., Serves, S., Feldmann, J. and Cullen, W.R. (1997) Determination of antimony species with high-performance liquid chromatography using element specific detection. Fresenius J. Anal. Chem., 359, 484-491. 

The most suitable techniques for the rapid, accurate determination of the elemental content of foods are based on analytical atomic spectrometry, for example, atomic absorption spectrometry (AAS), atomic emission spectrometry (AES), and mass spectrometry, the most popular modes of which are Game (F), electrothermal atomization (ET), and hydride generation (HG) AAS, inductively coupled plasma (ICP), microwave-induced plasma (MIP), direct current plasma (DCP) AES, and ICP-MS. Challenges in the determination of elements in food include a wide range of concentrations, ranging from ng/g to percent levels, in an almost endless combination of analytes with matrix speci be matrices. 

Elemental speciation studies show that human milk, especially colostrum and transitional milk, is very rich in HMW species associated with metals. Of course, many more studies are needed for a reliable speciation of such HMW compounds. In this sense, validation approaches, both for the reliable identification and exact determination of such species, should be urgently developed. In the same way as the elemental composition and/or distribution of human milk can be considered ideal for feeding the newborn, the composition of formula milks for newborns should ideally be as similar as possible to maternal milk at every lactating stage. However, essential element speciation in formula milks is far from that of human milk (the ideal composition). This could explain why the bioavailability of essential elements (including Cu, Fe, I, Mn, Se, and Zn) from formula milk is much lower than from human milk. Hence, artificial formulas are usually supplemented with such essential elements. More scientific knowledge is definitely necessary on the composition (speciation) of such elements and more attention must be paid to the chemical form in which they are added to formula milks. 

F. Cubadda, Inductively coupled plasmaDmass spectrometry for the determination of elements and elemental species in food a review, Int. J. AOAC, 87 (2004), 173D204. 

The mass determination of ionic species (atomic or polyatomic ions) in mass spectrometry is always a comparative measurement, which means the mass of an ionic species is determined with respect to reference masses of elements (or substances) used for mass calibration. The reference mass is thus acquired from the mass unit (m = In = 1/12) of the mass of the neutral carbon isotope (m = 1.66 X 10 kg). A mass calibration is easy to perform in solid-state mass spectrometry if the sample contains carbon (using carbon cluster ions with whole masses, as discussed above). The so-called doublet method was apphed formerly, e.g., ions and doubly charged Mg + forming a doublet at the same nominal mass number 12 were considered, where they are slightly displaced with respect to one another. The doublet method is no longer of relevance in modern inorganic mass spectrometry. Orientation in the mass spectra can be carried out via the matrix, minor and trace elements after mass calibration and by comparing the measured isotopic pattern of elements with theoretical values. 

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