Speciation analysis quantitative

This example illustrates a range of problems that are symptomatic in quantitation and standardisation which appear in speciation analysis and in determination of organic compounds in solids. Organotin compounds (e.g. methyltin, butyltin, phenyltin) comprise one of the most thoroughly studied groups of organometallic compounds found in environmental samples. 

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). 

A simple and rapid procedure was developed for the simultaneous determination of methyl-Hg and Hg(II) in Psh CRMs [43], The procedure was based on a rapid MW-assisted solubilization of biomaterial with TMAH, simultaneous quantitative ethylation-extraction of the Hg species into hexane, Bash isothermal separation using minicolumns, and Pnal detection by MIP-AES. The method was validated for speciation analysis for HG using the BCR 463 and 464 Tuna Fish CRMs. 

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. 

Contemporary speciation analysis is developing in two main directions the search for new forms of elements and introduction of the principles of modem chemical metrology into day-to-day practice. Activities encompassed by the former area are qualitative, aimed at the release and identification of often previously undescribed substances involved in living processes that have not been clarified to date. The other area, which requires the introduction of good laboratory practice, comprises routine analyses (i.e., assaying defined element forms) in real-life materials. Although the importance of correct interpretation of quantitative results seems obvious today, it did not always enjoy the status it has today. 

The variety of physicochemical forms of arsenic and its well-demonstrated species-dependent toxicity have stimulated progress in speciation analysis of this element. A considerable number of analytical methods for the qualitative and quantitative analysis of... 

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 analysis has come a long way in the past 10 to 15 years with improvements in the instrumental and extraction hardware leading to faster methods with better accuracy and precision even at low analyte concentrations. The wide range of CRM and the greater availability of the standards and reagents commonly used for speciation analysis have helped to improve the results. Future advances are required in the provision of methods that provide quantitation with structural characterization simultaneously, which will improve confidence in the speciation results. A recent perspective article by one of the early pioneers in chemical speciation analysis discusses the future of the area, in the context of the initial work in the subject. 

CE-MS has been used in analyses of anions and cations as a method simultaneously providing positive identification and quantitation. CE-ESI MS is particularly well suited for analyses of quaternary ammonium salts. Speciation analysis of As can be carried out using a CE-ICP-MS. Problems in interfacing the ICP-MS detection to CE are associated with low flow rates and small samples analyzed. Detection limits in ppb region can be attained, using postcapillary hybridization prior to ICP-MS. 

Instrumentation for speciation requires the ability to quantitatively determine various chemical species of an element. The most widely used instrumental configuration includes a system to separate the chemical species, such as chromatography or electrophoresis, and an atomic spectrometry detectoi which provides high sensitivity and specificity for the separated compounds of the element of interest. Figure 1 illustrates instrumentation that was employed for manganese speciation analysis. 

Of course, since H may be incorporated in the micas structure in various ways, the SIMS technique may be successfully complemented by FTIR, and particularly by micro-FTIR, because the latter technique is an aid in the determination of hydrogen speciation. However, quantitative analysis of H by SIMS is important when site population, and then crystal chemical formulae, have to be derived. 

The ability to measure the concentration of the exact form of the analyte present in the sample yields important information regarding the chemical and biological reactivity of the material. Because of the significant differences in toxicity between various forms of trace elements in the sample, occurrence standards are often estabhshed by regulatory agencies specific to a particular form of the analyte. This speciation analysis approach provides the information required to study and monitor these toxic compounds. In addition, to determine the fate of specific compounds in chemically reactive situations, quantitative information about the specific forms of the materials present is required to understand the process chemistry and kinetics that are occurring. 

As speciation analysis slowly enters authority s regulations (already the case for chromium, organotin and methylmercury species) and routine analysis becomes required, precise and accurate quantitative species determination, as well as access to certified reference materials, is becoming imperative. 

In general, ICP-MS is a sensitive and selective detector for speciation analysis however, spectroscopic interferences can cause problems for quantitative determination of an analyte, as well as for species identification based on the analyte s isotopic pattern. Spectroscopic interferences by another element (isobaric interferences) can often be corrected for using equations involving the known natural isotopic distribution of the interferent and the analyte. Polyatomic interferences, on the other hand, are less easily evaluated and compensated for. The source of these interferences is often the plasma (e.g. At2+) or a combination of the plasma and the sample or separation medium (e.g. ArCl+). Both the collision cell (CC) and the dynamic reaction cell (DRC) are designed to reduce the effect of spectroscopic interferences on the determination of the elements of interest. 

Instrumental Quantitative Analysis. Methods such as x-ray spectroscopy, oaes, and naa do not necessarily require pretreatment of samples to soluble forms. Only reUable and verified standards are needed. Other instmmental methods that can be used to determine a wide range of chromium concentrations are atomic absorption spectroscopy (aas), flame photometry, icap-aes, and direct current plasma—atomic emission spectroscopy (dcp-aes). These methods caimot distinguish the oxidation states of chromium, and speciation at trace levels usually requires a previous wet-chemical separation. However, the instmmental methods are preferred over (3)-diphenylcarbazide for trace chromium concentrations, because of the difficulty of oxidizing very small quantities of Cr(III). 

Applications Table 8.58 shows the main fields of application of inorganic mass spectrometry. Mass-spectrometric techniques find wide application in inorganic analysis, and are being used for the determination of elemental concentrations and of isotopic abundances for speciation and surface characterisation for imaging and depth profiling. Solid-state mass spectrometry is usable as a quantitative method only after calibration by standard samples. 

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