Standardized procedures sometimes define each detail

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Standardized procedures sometimes define each detail from instrument type to be used up to the reproducibility of the final results. Typically, the following items are included: Method, instrument and measurement process; Standard samples and sample preparation; Calculation methods; Precision of results. A closer look at typical specifications will help to understand the advantages and drawbacks of standardized methods. Method, Instrument, and Measurement Process A standardized method will specify X-ray fluorescence in general or, more specifically, an energy-dispersive (EDX) or a wavelength-dispersive spectrom- eter (WDX). Sometimes EDX or WDX is not stated explicitly, but follows from the description of the instrument details. Such instrument details can include the anode material and the minimum power of the X-ray tube, the analyzer crystal to be used in a wavelength- dispersive system or the specific kind of detector. The more detailed these descriptions, the higher is the risk to exclude new developments. For example, a modern medium-power wavelength-dispersive spectrometer with a sealed proportional detector may easily outperform old high-power instruments, but will possibly not fulfill the specifications of a minimum tube power and a flow proportional counter. For future standardized methods, it may be more ap- propriate to define parameters, which are directly relevant for the quality of the results, e.g., the minimum counting statistical error or the minimum reso- lution of a detector instead of technical specifications subject to innovations. Standardized methods typically specify the X-ray line to be used and spe- cial measurement parameters like the energy or wavelength for background measurements. Sample Preparation and Standard Samples Typically, an X-ray spectrometer sees only some milligrams of material close to the surface of the specimen. As an important precondition for reliable results, this volume has to be representative of the material to be analyzed. Therefore, all standardized methods describe sample preparation in detail including, e.g., the purity of reagents to be used.
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402 K.-E. Mauser Many standardized methods deal with the analysis of liquid samples or materials prepared as fused beads. For these applications synthetic standards can be used. The standardized methods prescribe in detail how to mix these standards by using pure reagents. When such synthetic standards are prepared exactly as defined, various laboratories will base their calibrations on exactly the same kind of standards and therefore ensure consistency of results. Sometimes certified reference materials are an option or have to be used. These materials have to be acquired from a national standards body or an accredited supplier.
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  • Spring '14
  • MichaelDudley

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