[B._Beckhoff,_et_al.]_Handbook_of_Practical_X-Ray_(b-ok.org).pdf

2 using direct analysis the risks of contamination

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2 . Using direct analysis, the risks of contamination and the loss of material to be analyzed are reduced. Differ- ent reflector materials were investigated as impaction plates. Injuk and Van Grieken [356] investigated the detection limits for quartz glass, siliconized quartz glass, and plexiglass reflectors, where the siliconized quartz glass re- flectors were prepared by dispersing a drop of silicon solution on the quartz glass surfaces. Their results indicated that the use of quartz glass carriers provided the best detection limits. Among different reflector materials, the use of polished silicon substrates have been evaluated by Esaka et al. [357]. They pointed out that an important factor determining the detection limits achievable by the reflectors is their surface roughness. The detection limits of elements for the polished Si carriers in TXRF analysis were superior to those for glassy carbon (two orders of magnitude) and even for quartz glass carri- ers (three times, see Fig. 7.120). Molybdenum anode X-ray tube operating at 40 kV and 40 mA was used for irradiation of the samples. Si carriers were used for the elemental analysis of aerosol particles collected at Ibaraki, Japan from January to November 2002. From the variations in the elemental concentrations with time, the origin of the particles was deduced. Four groups of elements could be distinguished, which could be related to crustal, yellow dust, and anthropogenic sources, because of the availability of size-segregated samples. The Si-wafer substrates were also used as impaction surfaces by T¨or¨ ok et al. [358]. For particles smaller than 0.5 µ m, 0.02 m 3 of air was sufficient for TXRF analysis of low- Z elements at the BESSY synchrotron source. Also it was feasible to investigate the chemical environment of nitrogen using TXRF- NEXAFS from nanoscopic amount of material. This capability can improve the time resolution to below 10 min that is commonly expected from air quality monitoring devices of “classical pollutants” such as SO 2 , NO X , PM 10 . There is of course the inherent limitation of SR measurement that the sample number that can be analyzed is very restricted.
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Methodological Developments and Applications 627 Fig. 7.120. The detection limits of elements for the glassy carbon, the quartz glass, and the Si carriers. Reproduced from Esaka et al. [357] by permission of Elsevier Science B.V. 7.5.4 Monte Carlo Based Quantitative Methods for Single Particles Many environmental applications demand for the quantitative characteriza- tion of particulate matter. There are two major approaches in the analysis of particulate matter: bulk and single-particle analysis. By using bulk methods, only the average composition of the particulate sample can be obtained. How- ever, these samples are heterogeneous mixtures of different types of particles, so the average composition and average diameter do not describe well the dispersion of the particles in the sample. In order to derive environmentally relevant information on the sources of the environmental particles like aerosols,
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  • Spring '14
  • MichaelDudley

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