Speciation Analysis of Elements

Speciation refers to the different physical and chemical forms of an element in a sample. Speciation analysis involves identifying the physical and chemical forms of an element and their determination in a sample. 

Most legal regulations in force worldwide are based on overall levels of elements in food products only a few concern particular forms of elements. Organisations such as the Environmental Protection Agency (EPA), World Health Organisation (WHO), European Environmental Commission (EEC) and US Eood and Drug Administration (USEDA) have recognised the importance of speciation analysis and proposed limits to contamination by various forms of elements (e.g. As, Hg and Sn) [8, 172]. 

The consecutive steps in speciation analysis are sample collection, sample conservation and storage, elimination of counterfeit samples, extraction/mineral-isation, derivatisation, separation, detection, calibration, calculation of results and evaluation of results [212, 234, 235]. 

The application of speciated isotope dilution mass spectrometry (SIDMS) in speciation analysis was described and discussed by Huo et al. [236]. According to Encinar [237], isotopic analysis of a solution can be used to evaluate the application of various speciation forms of elements in food and in medications. 

From the analytical point of view, certified reference materials play a vital role in food monitoring, as they permit quality and measurement accuracy to be assessed. The need to apply such materials in monitoring the quality of speciation analysis measurements was justified by Quevauviller [182] and Emons [238]. 

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Progress in the fractionation and speciation analysis of elements with the use of extraction is still far from needs and expectations, undoubtedly as a result of the insignificant/insufficient number and small diversity of available reference materials. 

For many years FIA methods have found wide application in speciation analysis of elements in different matrices. In contrast to chromatography, it usually requires development of rather complex procedures and construction of an instrumental setup in order to obtain a suitable combination of the separation and conversion steps. A short time for carrying out those operations in the FIA manifold is advantageous in terms of avoiding the shift of chemical equilibria during the speciation measurement (Campanella et al., 1996 Cerda and Estela, 2005). Relatively simple if achievable, it seems to be a parallel application of several selective detectors allowing simultaneous... 

The compounds MMA, DMA, and TMAO are reduced in acidic aqueous media by borohydride solutions to methylarsine (MeAsH2, bp 2°C), dimethylarsine (Me2AsH, bp 35°C), and trimethylarsine (Me3As, bp 55°C), respectively. These products are useful derivatives for speciation analysis of arsenic because they are readily separated from complex sample matrices and may be further separated from each other by distillation (41) or by gas chromatography (42) prior to their determination by element-specific detectors. Consequently, arsine generation techniques are the most commonly used methods for determining MMA, DMA, and TMAO in marine samples. 

In 2006, Lobinski et al.1 reported on the imaging and speciation analysis of trace elements to study the element distribution, oxidation state, metal site and metal structure in biological environments using mass spectrometric techniques (LA-ICP-MS, SIMS, MALDI-MS) and non-mass-spectrometric techniques such as micro-PIXE (proton induced X-ray emission), XANES (X-ray absorption near edge structure) and EXAFS (extended X-ray absorption fine structure) -the latter two techniques are very sensitive due the use of a more intense synchrotron beam.1... 

Chau, Y.K. and Wong, P.T.S., 1983. Direct speciation analysis of molecular and ionic organometals. In G.G. Leppard (ed.), Trace Element Speciation in Surface Waters. Plenum, New York, pp. 87-102. 

Quevauviller, Ph. (2000) Certified reference materials a tool for quality control of elemental speciation analysis. In Elemental Speciation - New Approaches for Trace Element Analysis (eds Sutton, K.L. and Caruso, JA.). Elsevier, Amsterdam, 531-569. 

Quevauviller, Ph., Maier, EA. and Griepink, B. (eds) (1996a) Quality control of results of speciation analysis. In Element Speciation in Bioinorganic Chemistry (ed. Caroli, S.). John Wiley and Sons, Chichester. 

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. 

J. Szpunar, Trace element speciation analysis of biomaterials by high performance liquid chromatography with inductively coupled plasma mass spectrometric detection (HPLC-ICP MS), Trends Anal. Chem., 19 (2000), 127D137. 

Sample preparation methods for the speciation analysis of As and Se have been improving almost at the same pace as the development of speciation methods for other elements. In the case of As, the study by Braman and Foreback [3] was one of the first key experiments, while path-finding Se speciation analyses were conducted during the 1960s, among others by Martin and Cummins [4], Afterwards, each new sample preparation method that was proved to be suitable for speciation purposes (i.e., that did not alter the chemical species of a given sample) was taken as a reference for the next step ahead. This feedback process... 

Aluminium is an environmentally abundant element and has no known biological function in living cells. On the other hand, A1 exhibits biological toxicity as demonstrated in experimental models." " Intake and output of aluminium for the healthy population from various sources, biological monitoring of occupational aluminium exposure in serum and speciation analysis of the amount and composition of A1 species with high and low molecular masses, have been reviewed by several groups. Besides the use of mass spectrometric and non-mass spectrometric techniques (e.g., ETAAS after separation of human serum proteins ) ESI-MS-MS analysis has also been performed to identify the A1 species. 

Anion exchange chromatography coupled with ICP MS was used in the simultaneous speciation analysis of As, Se, Sb and Te compounds in extracts of fish [230]. Size exclusion chromatography (SEC) coupled with specific detectors is frequently used to analyse species of trace elements in protein-rich materials, such as extracts of meat and plant tissues. For instance, SEC hyphenated with ICP MS was used for the speciation analysis of Cu and Zn in samples of leguminous plants [191]. The same technique was applied to the speciation analysis of Cu, Cd, Zn, Se, As and Ca in fish [220] and Fe, Zn, Cu, Ag, Cd, Sn and Pb in mussels [189]. SEC HPLC coupled with GF AAS mmed out to be very useful for determining levels of Fe species in baby food [312]. With gel permeation chromatography (GPC) GF AAS, the speciation forms of Cd were determined in two kinds of vegetables contaminated with this element [216]. 

Richarz, A.-N., Bratter, P. Speciation analysis of trace elements in the brain of individuals with Alzheimer s disease with special emphasis on metallothioneins. Anal. Bioanal. Chem. 372, 412-417 (2002)... 

Detection techniques of high sensitivity, selectivity, and ease of coupling with sample preparation procedures are of special interest for measuring PGM content in biological and environmental samples. ICP MS, electrothermal atomic absorption spectrometry (ET AAS), adsorptive voltammetry (AV), and neutron activation analysis (NAA) have fotmd the widest applications, both for direct determination of the total metal content in the examined samples and for coupling with instrumental separation techniques. Mass spectrometry coupled with techniques such as electrospray ionization (ESI) and capillary electrophoresis (CE) (e.g., ESI MS", LC ESI MS", LC ICP MS, CE MS", and CE ICP MS) offer powerful potential for speciation analysis of metals. MS is widely used for examination of the distribution of the metals in various materials (elemental analysis) and for elucidation of the... 

Q. Tu, T. B. Wang, X. Jia, and X. Bn, Speciation analysis of halogenides and oxyhalogens by ion chromatography with inductively coupled plasma mass spectrometer as element-specific detector, Merck Research Laboratories internal communication. 

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