Speciation sampling

On the basis of the preceding discussion, it should be obvious that ultratrace elemental analysis can be performed without any major problems by atomic spectroscopy. A major disadvantage with elemental analysis is that it does not provide information on element speciation. Speciation has major significance since it can define whether the element can become bioavailable. For example, complexed iron will be metabolized more readily than unbound iron and the measure of total iron in the sample will not discriminate between the available and nonavailable forms. There are many other similar examples and analytical procedures that must be developed which will enable elemental speciation to be performed. Liquid chromatographic procedures (either ion-exchange, ion-pair, liquid-solid, or liquid-liquid chromatography) are the best methods to speciate samples since they can separate solutes on the basis of a number of parameters. Chromatographic separation can be used as part of the sample preparation step and the column effluent can be monitored with atomic spectroscopy. This mode of operation combines the excellent separation characteristics with the element selectivity of atomic spectroscopy. AAS with a flame as the atom reservoir or AES with an inductively coupled plasma have been used successfully to speciate various ultratrace elements. 

Multielement analysis will become more important in industrial hygiene analysis as the number of elements per sample and the numbers of samples increases. Additional requirements that will push development of atomic absorption techniques and may encourage the use of new techniques are lower detction and sample speciation. Sample speciation will probably require the use of a chromatographic technique coupled to the spectroscopic instrumentation as an elemental detector. This type of instrumental marriage will not be seen in routine analysis. The use of Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) (17), Zeeman-effect atomic absorption spectroscopy (ZAA) (18), and X-ray fluorescence (XRF) (19) will increase in industrial hygiene laboratories because they each offer advantages or detection that AAS does not. 

Several types of sampling tasks could involve various types of extraction at the sampling site. This would be the case in integrating sampling, where the mean concentration over a period or over an area is sought, or when a speciation sampling is attempted, i.e., where the aim is to determine not only total concentrations but also equilibria (dissolved-bound, different dissociation conditions, different redox conditions, etc.). 

The speciation scheme of Batley and Florence requires eight measurements on four samples. After removing insoluble particulates by filtration, the solution is analyzed for the concentration of anodic stripping voltammetry (ASV) labile metal and the total concentration of metal. A portion of the filtered solution is passed through an ion-exchange column, and the concentrations of ASV metal and total metal are determined. A second portion of the filtered solution is irradiated with UV light, and the concentrations of ASV metal... 

Determine the speciation of each metal in this sample of sea water. 

The objective ia any analytical procedure is to determine the composition of the sample (speciation) and the amounts of different species present (quantification). Spectroscopic techniques can both identify and quantify ia a single measurement. A wide range of compounds can be detected with high specificity, even ia multicomponent mixtures. Many spectroscopic methods are noninvasive, involving no sample collection, pretreatment, or contamination (see Nondestructive evaluation). Because only optical access to the sample is needed, instmments can be remotely situated for environmental and process monitoring (see Analytical METHODS Process control). Spectroscopy provides rapid real-time results, and is easily adaptable to continuous long-term monitoring. Spectra also carry information on sample conditions such as temperature and pressure. 

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). 

Sources of analysed samples 830 Spark source 764 Speciation 4... 

The advantages of controlled-potential techniques include high sensitivity, selectivity towards electroactive species, a wide linear range, portable and low-cost instrumentation, speciation capability, and a wide range of electrodes that allow assays of unusual environments. Several properties of these techniques are summarized in Table 1-1. Extremely low (nanomolar) detection limits can be achieved with very small sample volumes (5-20 pi), thus allowing the determination of analyte amounts of 10 13 to 10 15 mol on a routine basis. Improved selectivity may be achieved via the coupling of controlled-potential schemes with chromatographic or optical procedures. 

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). 

Cornelis R (1996) Involvement of analytical chemistry in chemical speciation of metals in clinical samples. Ann Clin Lab Sd 26 252-263. 

Cornelis R, De Kimpe J, and Zhang X (1998) Trace elements in clinical samples revisited -speciation is knocking at the door. Sample preparation, separation of the spedes and measurement methods. Spectrochim Acta 536 187-196. 

Morabito R, Chiavarini S, and Cremisini C (1995) Speciation of organotin compotmds in environmental samples by GS-MS. In Qltevauviller Ph, Maier EA and Griepink B, eds. Quality Assurance for Environmental Analysis, pp 437-462. Elsevier, Amsterdam. 

Pyrzynska K (1996) Organolead speciation in environmental samples a review. Mikrochim Acta 122 279-293. 

Veecoutere K, and Cornelis R (1995) Chromium speciation in environmental and biological samples. In Quality Assurance for Environmental Analysis, Qubvauviller Ph, Maiee EA and Geiepink B, eds. pp 195-213. Elsevier, Amsterdam. 

Solid sampling is, so far, the only method that allows the speciation of Mg contained in metals and other materials. At a temperature of i8oo°C, the metalhc Mg is completely vaporized and e.g. MgO appears at 28oo°C. So, RMs or synthetic sample mixtures can be analyzed to prepare new RMs (Ohls 1981). 

Presently, the precise determination of the true dissolved Th fraction in water samples remains a challenge. Results from ultrafiltration experiments on organic-rich water samples from the Mengong river tend to demonstrate that Th concentration is less than 15 ng/L in absence of DOC (Table 2 and Viers et al. 1997), and that Th is still controlled by organic carbon in the final filtrate of the ultrafiltration experiments. The latter conclusion is also supported by the results obtained for the Kalix river (Porcelli et al. 2001). These results therefore not only raised the question of the determination of the amount of dissolved Th in water but also of the nature of Th chemical speciation. 

Lujaniene G, Lujanas V, Jankunaite D, et al. 1999. Speciation of radionuclides of the Chernobyl origin in aerosol and soil samples. J Environ Radioact 49 107-114. 

Table 7.33 reports the main characteristics of GC-ICP-MS. Since both GC and ICP-MS can operate independently and can be coupled within a few minutes by means of a transfer line, hyphenation of these instruments is even more attractive than GC-MIP-AES. GC-ICP-MS is gaining popularity, probably due to the fact that speciation information is now often required when analysing samples. Advantages of GC-ICP-MS over HPLC-ICP-MS are its superior resolution, resulting in sharper peak shapes and thus lower detection limits. GC-ICP-MS produces a dry plasma when the separated species reach the ICP they are not accompanied by solvent or liquid eluents. This reduces spectral interferences. Variations on the GC-ICP-MS... 

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