Speciation, analysis

Low molecular weight Middle molecular weight High molecular weight  

Degree of polymerization number n Molecular weight [Da] Viscosity [cSt] D pveof polymerization number n Molecular weight [Da] Viscosity [cSt] Degree of polymerization number n Molecular weight [Da] Viscosity [cSt] 

Structure Name of PDMS Molecular weight LogP Lipinski s rule of five 

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SPECIATION ANALYSIS OF MATERIALS BASED ON INORGANIC COMPOUNDS OF LANTHANIDES... 

The proposed method can be applied to the speciation analysis of environmental solids for risk assessment of their contaminants as well as to design of effective leaching schemes. 

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. 

In the case of soluble samples such as fish, mussels, etc. the speciation analysis has been achieved most successfully (e.g. Quevauviller et al. 1996a). 

A major share of elemental analysis will eventually evolve into speciation analysis. 

The list of elements and their species listed above is not exhaustive. It is limited to the relatively simple compounds that have been determined by an important number of laboratories specializing in speciation analysis. Considering the economic importance of the results, time has come to invest in adequate CRMs. There is a steadily increasing interest in trace element species in food and in the gastrointestinal tract where the chemical form is the determinant factor for their bioavailability (Crews 1998). In clinical chemistry the relevance of trace elements will only be fully elucidated when the species and transformation of species in the living system have been measured (ComeUs 1996 Cornelis et al. 1998). Ultimately there will be a need for adequate RMs certified for the trace element species bound to large molecules, such as proteins. 

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. 

Lobinski R, Dirkx WMR, Szpunar-Lobinski J, and Adams F (1995) Speciation analysis of orga-nolead compounds. Status and future prospects. In Quevauvillee Ph, Maier EA and Grie-ptNK B, eds. Quality Assurance for Environmental Analysis, pp 319-356. Elsevier, Amsterdam. 

Quevauviller Ph (1998) Requirements for production and use of certified reference materials for speciation analysis a European Commission perspective. Spectrodiim Acta 536 1261-1279. Quevauviller Ph, and Horvat M (1999) Artifact formation of methylmercury in sediments. Anal Chem, Letter to the Editor 7i i55A-i56A. 

Various forms of off- and on-line AES/AAS can achieve element specific detection in IC. The majority of atomic emission techniques for detection in IC are based on ICP. In the field of speciation analysis both IC-ICP-AES and IC-ICP-MS play an important role. Besides the availability of the ICP ion source for elemental MS analysis, structural information can be provided by interfaces and ion sources like particle beam or electrospray. 

SFC-ICP-MS requires rather expensive and complicated instrumental design [473,474]. Interfacing the SFC restrictor with the ICP torch follows different approaches for pSFC and cSFC [469]. Polar modifiers, however, do not have a serious deleterious effect on the ICP plasma, which enables the polarity of the mobile phase to be changed with no significant loss of sensitivity or resolution. This enables analysis of compounds which are too polar for adequate separation with pure C02 as the mobile phase. SFC is still in its infancy as far as speciation analysis of metal-containing additives is concerned. 

The artificial separation between organic and inorganic mass-spectrometric methods is now narrowing, as shown by speciation studies (Section 8.8). Plasma-source MS (PS-MS), mainly as ICP-MS and MIP-MS, has been particularly effective when applied to speciation analysis. Direct speciation is also possible with electrospray MS (ESI-MS). 

Speciation involves a number of discrete analytical steps comprising the extraction (isolation) of the analytes from a solid sample, preconcentration (to gain sensitivity), and eventually derivatisation (e.g. for ionic compounds), separation and detection. Various problems can occur in any of these steps. The entire analytical procedure should be carefully controlled in such a way that decay of unstable species does not occur. For speciation analysis, there is the risk that the chemical species can convert so that a false distribution is determined. In general, the accuracy of the determinations and the trace-ability of the overall analytical process are insufficiently ensured [539]. 

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... 

With the exception of GC-MIP-AES there are no commercial instruments available for speciation analysis of organometallic species. Recently, a prototype automated speciation analyser (ASA) for practical applications was described [544,545], which consists of a P T system (or focused microwave-assisted extraction), multicapillary GC (MC-GC), MIP and plasma emission detection (PED). MCGC-MIP-PED provides short analysis times ([Pg.676]

Mass spectrometry can be specific in certain cases, and would even allow on-line QA in the isotope dilution mode. MS of molecular ions is seldom used in speciation analysis. API-MS allows compound-specific information to be obtained. APCI-MS offers the unique possibility of having an element- and compound-specific detector. A drawback is the limited sensitivity of APCI-MS in the element-specific detection mode. This can be overcome by use of on-line sample enrichment, e.g. SPE-HPLC-MS. The capabilities of ESI-MS for metal speciation have been critically assessed [546], Use of ESI-MS in metal speciation is growing. Houk [547] has emphasised that neither ICP-MS (elemental information) nor ESI-MS (molecular information) alone are adequate for identification of unknown elemental species at trace levels in complex mixtures. Consequently, a plea was made for simultaneous use of these two types of ion source on the same liquid chromatographic effluent. 

For chemical speciation, X-ray absorption spectroscopy is another supreme tool taking advantage of its electronic and structural information power. Also, REMPI-MS is outstanding in its selectivity for molecular species. Radioanalytical methods have also been used for speciation analysis [548]. Microscopical speciation analysis requires SSIMS or LMMS [549]. 

Table 8.80 shows the present status of speciation methodology. For trace-metal speciation, atomic absorption detectors feature a relatively high absolute detection limit (10 pg level), as compared to the 0.1 to 1 pg sensitivity level for molecular ion MS techniques as well as for MIP-AES. The detection limit of LEI-ToFMS is in the attogram range. Speciation has been reviewed [550]. Various monographs deal with speciation analysis [542,551,552]. 

Applications Speciation analysis is particularly important in plant and animal biochemistry and nutrition (food/food supplements), clinical biochemistry, industrial chemistry and environmental chemistry. In the... 

Kolasa et al. [562] have reported changes in the degree of oxidation of chromium (from Cr6+ to Cr3+) in the course of probe mineralisation of PE for AAS analysis. HPLC-ICP-MS has been used as a selenium-specific detector [563]. Other selenium speciation work by ICP-MS has been reported [564]. Numerous other examples of speciation analysis have been described for the most appropriate techniques (Chapter 7). 

Speciation analysis of organometal compounds by means of GC-MIP-AES and GC-ICP-MS has been reviewed [565], as has as metal speciation by HPLC... 

Ph. Quevauviller, Methods Performance Studies for Speciation Analysis, The Royal Society of Chemistry, Cambridge (1998). 

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