Total reflection x-ray fluorescence TXRF

Three techniques involving the use of X-ray emission to obtain quantitative elemental analysis of materials are described in this chapter. They are X-Ray Fluorescence, XRF, Total Reflection X-Ray Fluorescence, TXRF, and Particle-Induced X-Ray Emission, PIXE. XRF and TXRF use laboratory X-ray tubes to excite the emission. PIXE uses high-energy ions from a particle accelerator. 

Prange et al. [809,810] carried out multielement determinations of the stated dissolved heavy metals in Baltic seawater by total reflection X-ray fluorescence (TXRF) spectrometry. The metals were separated by chelation adsorption of the metal complexes on lipophilised silica-gel carrier and subsequent elution of the chelates by a chloroform/methanol mixture. Trace element loss or contamination could be controlled because of the relatively simple sample preparation. Aliquots of the eluate were then dispersed in highly polished quartz sample carriers and evaporated to thin films for spectrometric measurements. Recoveries (see Table 5.10), detection limits, and reproducibilities of the method for several metals were satisfactory. 

Total reflection x-ray fluorescence (TXRF) has become very popular for the conduct of microanalysis and trace elemental analysis [77-79]. TXRF relies on scatter properties near and below the Bragg angle to reduce background interference, and to improve limits of detection that can amount to an order of magnitude or moreover more traditional XRF measurements. As illustrated in Fig. 7.18, if x-rays are directed at a smooth surface at a very small angle, virtually all of the radiation will be reflected at an equally small angle. However, a few x-rays will excite atoms immediately at the surface, and those atoms will emit their characteristic radiation in all directions. One obtains very clean... 

Lagarde P, Delaunay R, Flank AM, Jupille J (1993) Site of sulfur impurities in silicate glasses and REFLEXAFS studies around the Si -edge. Jap J Appl Phys 32 619-621 Lee PA, Citrin PH, Eisenberger PM (1981) Extended X-ray absoption fine structure-its strength and limitations as a structural tool. Rev Mod Phys 53 769-806 Lee JM, Yoo H-H, Joo M (1999) Numerical determination of a true absorption spectrum from grazing-incidence fluorescence EXAFS data. J Synchrotron Rad 6 244-246 Lieser KH, Flakowski M, Hoffman P (1994) Determination of trace elements in small water samples by total reflection X-ray fluorescence (TXRF) and by neutron activation analysis (NAA). Fresenius J Anal Chem 350 135-138... 

In order to evaluate possible hazards for the enviroiunent and human health it is crucial to develop analytical strategies for fast and easy quantification of traces and ultra-traces of Pd in environmental matrices as well as biological tissues and fluids. Despite the efforts of numerous workgroups, a reliable method for the determination of Pd in all environmental matrices has yet to be developed. Up to date, the most important analytical methods for this task are electrothermal atomic absorption spectrometry (ETAAS), inductively coupled plasma-mass spectrometry (ICP-MS) and isotope dilution (ID)-ICP-MS, also strategies involving inductively coupled plasma-atomic emission spectrometry (ICP-AES), and electrochemical methods like anodic stripping voltammetry (ASV) have been described. Furthermore, total reflection X-ray fluorescence (TXRF) and instrumental neutron activation analysis (INAA) have been successfully employed for the determination of PGE in enviromnental matrices. 

Generally, the sensitivity of X-ray spectrometrie methods is not suffieient for direct measurement of PGE in environmental samples. However, adequate total reflection X-ray fluorescence (TXRF) methods have been developed to enable, after adequate sample preparation and analyte enrichment via Hg-coprecipitation, PGE-determination in various samples like road dust, airborne particles or liver and kidney tissue of exposed European eels (Anguilla anguilla) (Messerschmidt et al. 2000 Sures et al. 2001). 

Total reflection X-ray fluorescence (TXRF) spectrometry is a trace elemental microanalysis technique based on conventional energy dispersive X-ray fluorescence. It has become increasingly popular in the last decade and is applied in almost every field of trace elemental analysis where low detection limits and multielement capabilities are required. Like all X-ray techniques, TXRF is nondestructive making it extremely useful and important in areas where samples are precious and/or need to be used for further characterization. New tabletop instruments make this technique affordable and more versatile as it can be used also for field research. In the semiconductor industry, TXRF is now routinely applied to scan wafers for impurities on the surface and in near-surface layers. The following article introduces the basic principle of TXRF and its instrumental features and discusses various applications of this technique. 

VPD is also used in conjunction with total reflection X-ray fluorescence (TXRF) [33]. The surface contaminants are effectively preconcentrated by a factor of around 100 the exact value depends on the wafer size [34]. The wafer is placed on an optionally water-cooled... 

S. Woelfl, M. Mages, S. Mercado, L. Villalobos, M. Ovari, and F. Encina. Determination of trace elements in planktonic microcrustaceans using total reflection X-ray fluorescence (TXRF) First results from two Chilean lakes. Analytical and Bioanalytical Chemistry 378 1088-1094,2004. 

Surface analytical techniques can be classified in terms of the excitating and emitted probe cfr. Table 4.4). The penetration of the physical probe increases fl om ions (ISS, RBS, SIMS) to electrons (XPS) and finally photons (UV/VIS, IR, XRF, etc.). Amongst the photon beam techniques which show some degree of surface sensitivity, in practice only XPS, total reflection X-ray fluorescence (TXRF) and laser-induced mass spectroscopic methods (LMMS),... 

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