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

Regarding the sample preparation unfiltered samples

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a level of minimum or zero risk. Regarding the sample preparation, unfiltered samples may be more appropriate for health-related studies, as most of the particulate matter will ultimately yield bioavailable concentrations of heavy metals in the hydrochloric acid digestion system, that is, the human stomach. Again, trace metal concentrations in drinking water are shown in a broad range, depending on the source of water (lakes, rivers, etc.) or the way of transport. For example, concentrations of Pb in drinking water vary greatly,
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Methodological Developments and Applications 607 related particularly to the presence of lead in the plumbing system. This fea- ture is taken into account by the US EPA regulation, 1 setting an action level at 15 ppb and similarly with EC regulation at 10 ppb. The objective of the European Commission is to simplify the many individual directives covering water into a Water Resources Framework Directive. The EC Drinking wa- ter Directive 80/778/EEC has been updated in 98/83/EC and can be found on the WWW. 2 Also the World Health Organization (WHO) guidelines are public with many other relevant data. 3 From the above summary one can conclude some basic requirements for the analytical methods being used for water analysis. The most important are that the method should be a multielemental one if possible, exhibit a wide dynamic measurement range and be free from matrix effect along with a detec- tion limit (DL) at least of ppb. The analytical methods most commonly used for such tasks are atomic absorption spectrometry (AAS) or inductively cou- pled plasma mass spectrometry (ICP-MS). As it will be discussed later, total reflection X-ray fluorescence (TXRF) method has performance characteristics very similar to that of inductively coupled plasma atomic emission spectrom- etry (ICP-AES). The next paragraphs will demonstrate that only the TXRF method meets the above requirements, while the conventional XRF has serious limitations and can be applied only in combination with preconcentration. Preconcentration and matrix removal may be required where the concen- trations of elements in the water samples are particularly low and the interfer- ences caused by the matrix dominate any direct analysis. This is especially the case for conventional XRF due to its moderate sensitivity and high detection limits. From the point of view of trace metal analysis, salt content repre- sents the matrix and it is detrimental owing to the strong absorption effect caused in both exciting and fluorescence radiation. Actually, salt removal is performed together with preconcentration, making it a difficult problem when extremely efficient salt separation is needed with a quantitative trace metal re- covery. There is a large selection of materials for separation-preconcentration: activated carbon, liquid extraction, polyurethane foam loaded with chelating agents, ion-exchange to mention only those that are most popular (see also Chap. 6). There is a trend in analytical methods for water analysis with a greater use of solid-phase extraction (SPE) [281]. Naturally, new SPE mate-
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  • Spring '14
  • MichaelDudley

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