Sample for speciation analysis

Szpunar, J., Schmitt, VO., Donard, O.F.X. and Lobinski, R. (1996) Low-power focussed microwave technology as a new tool for rapid preparation of solid samples for speciation analysis. Trends Anal. Chem., 15, 181-187. 

G. E. Batley, Collection, preparation and storage of samples for speciation analysis, in G. E. Batley (Ed.), Trace Element Speciation Analytical Methods and Problems (1990), CRC Press, Boca Raton, Florida, 1-24. 

The main steps in preparing samples for speciation analysis involve extraction, cleanup, and pre-concentration, although the requirement for each of these will be dependent on the analyte, the sample matrix, and the analytical method. The criteria for a successful protocol are that the analytes are quantitatively removed from the sample matrix, without loss of structural integrity, or formation of the chemical species of interest. These competing requirements are not always possible to fulfill, and decomposition, species rearrangement, and artifactual analyte formation have been reported as occurring during different parts of the determination. 

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]. 

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. 

Trends in mass spectrometry focus on the improvement of instrumentation, of several techniques in order to minimize sample volume, to improve sensitivity and to reduce detection limits. This is combined with increasing the speed of several analyses, with automation of analytical procedures and subsequently reducing the price of analysis. A minimizing of sample volumes means a reduction of waste volume with the aim of developing green chemistry . Furthermore, new analytical techniques involve a development of quantification procedures to improve the accuracy and precision of analytical data. Special attention in future will be given to the development of hyphenated mass spectrometric techniques for speciation analysis and of surface analytical techniques with improved lateral resolution in the nm scale range. 

Zhang, N., J.S. Suleiman, M. He, and B. Hu. 2008. Chromium (Ill)-imprinted silica gel for speciation analysis of chromium in environmental water samples with ICP-MS detection. Talanta 75 536-543. 

Pantsar-Kallio, M. and P.K.G. Manninen. 1999. Optimizing ion chromatography-inductively coupled plasma mass spectrometry for speciation analysis of arsenic, chromium and bromine in water samples. Int. J. Environ. Anal. Chem. 75 43-55. 

A rapid and simple MW-assisted digestion method with alkaline solution (TMAH or methanolic KOH solution) was developed for speciation analysis of inorganic Hg and methyl-Hg in biological tissues [41]. Extracts with quantitative recoveries of Hg species after the alkaline dissolution of the sample were directly analyzed by an automated on-line hyphenated system incorporating aqueous HG, cryogenic trapping, GC, and detection by A AS. The proposed method was validated by the analysis of biological CRMs (CRM 463, DORM-1, TORT-1) and one BCR sample from an interlaboratory study (Tuna Fish 2). 

Sample Preparation for Speciation Analysis by Liquid-Phase... 

The nutritional, chemical, biological, and toxicological properties of a chemical element are known to be critically dependent on the form in which it occurs in food. The recognition of this fact has spurred the development of species-selective (speciation) analytical methods for food additives and contaminants. According to the IUPAC s dehnition, speciation analysis deals with the analytical activities of identification and/or measurement of the quantities of one or more individual chemical species in a given sample [1], The analytical approach is usually based on the combination of a chromatographic separation technique with an element-specif>c detection technique. The former ensures that the analyte compound leaves the column unaccompanied by other species of the analyte element, whereas the latter enables a sensitive and specil>c detection of the target element. Coupled (also called hyphenated) techniques have become a fundamental tool for speciation analysis and have been discussed in many published reviews [2D6]. 

K. Wrobel, S. S. Kannamkumarath, K. Wrobel, J. A. Caruso, Environmentally friendly sample pretreatment for speciation analysis by hyphenated techniques, Green Chem., 5 (2003), 250D259. 

Apart from the development of a general method for the analysis of Hg species (see the previous section) during recent years, many applications have been developed and refined for seafood matrices. For the determination of Hg species in seafood, a wide range of methods primarily focus on the determination of Me-Hg. Some publications focus on selected aspects of sample pretreatment, while others deal with the features of the analytical instruments used. When higher detection power for speciation analysis is requested, GC-ICP-MS is often the method of choice. The procedure is based on three steps, as illustrated in Figure 22.3. 

J. Leenaers, W. van Mol, H. G. Infante, F. C. Adams, Gas chromatography-inductively coupled plasma-time-of-flight mass spectrometry as a tool for speciation analysis of organomercury compounds in environmental and biological samples, J. Anal. Atom. Spectrom., 17 (2002), 1492-1497. 

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... 

Fig. 4.23. Manifolds used for speciation analysis of solid samples. (A) Mercury speciation (as Hg- and PhHgH). (B) Nitrogen speciation (as ammonia and urea). GLS gas-liquid separator, MWS microwave system, ISE ammonia-selective electrode, RE reference electrode, WB water bath thermostat. Other abbreviations as in previous figures. (Reproduced with permission of Elsevier.)...

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. 

The Laboratory of Applied Analytical Chemistry at the Warsaw University, Chemistry Department works on environmental analytical chemistry, development of analytical methods for determination of trace metals in environmental samples and speciation analysis as a modem tool for environmental risk assessment. 

Fig. 3.1 Overview of complete consecutive analytical steps for speciation analysis of a sample, starting with sampling step and including quality control strategies. CRM = certified reference material.

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