Analytical techniques, concentration dissolution procedures

All geological materials can be dissolved quantitatively, and there is an extensive literature on the various processes available. The choice of dissolution procedure will vary according to the nature of the sample, the number and size of the samples, the requirements of the analytical technique in terms of analyte concentration and total dissolved solid concentration, volatility of the analytes of interest, precision and accuracy required, contamination from... 

The direct analysis of solid samples, independent of the analytical technique that is used for that purpose, has a number of distinct advantages over procedures that involve an acid digestion or other dissolution methods. Although the relative importance of the various aspects depends very much on the type of sample that has to be analyzed, the analyte that has to be determined and its concentration, and the specific requirements regarding speed of analysis, accuracy and precision, the following features are generally accepted ... 

Different analytical procedures have been developed for direct atomic spectrometry of solids applicable to inorganic and organic materials in the form of powders, granulate, fibres, foils or sheets. For sample introduction without prior dissolution, a sample can also be suspended in a suitable solvent. Slurry techniques have not been used in relation to polymer/additive analysis. The required amount of sample taken for analysis typically ranges from 0.1 to 10 mg for analyte concentrations in the ppm and ppb range. In direct solid sampling method development, the mass of sample to be used is determined by the sensitivity of the available analytical lines. Physical methods are direct and relative instrumental methods, subjected to matrix-dependent physical and nonspectral interferences. Standard reference samples may be used to compensate for systematic errors. The minimum difficulties cause INAA, SNMS, XRF (for thin samples), TXRF and PIXE. 

For determination of trace metals in human specimens it is not possible to state general valid regulations. Every clinical question signifies a separate analytical problem. The analytical procedure depends on the trace metal to be determined, the material, and the concentration of trace metal in the sample. However, AAS generally is limited to liquid samples, so that the material must be decomposed. Different decomposition techniques are used, e.g., wet ashing, pressure decomposition, microwave decomposition, and dry ashing followed by dissolution with water or acids [30]. Another disadvantage of AAS is the fact that within each series only one element can be determined. 

A report that summarizes the state-of-the-art analytical methods for assay of SNF was published by the Expert Group on Assay Data of Spent Nuclear Fuel (EGADSNF 2011). Their stated objective was to view the techniques that serve for destructive post-irradiation examination (PIE) for analysis of the isotopic composition and concentrations in spent nuclear fuel sample. First, the sampling procedures and sample dissolution methods are considered, followed by techniqnes for separating the radionuclides and the measurement procedures. However, it should be emphasized that... 

It is useful to compare various sampling methods to quantitative chemical analysis and to list their respective advantages and limitations (Table 6.3). In fact, an analysis is only as good as the sample which has been introduced into the analytical instrument. The ideal way to carry out a quantitative analysis with a sampling technique is to transfer an analyte completely from the sample matrix to the analytical apparatus. This means that in principle quantitative analysis of an additive is well carried out by dissolution (100% recovery), especially when the procedure restricts additional handling (evaporation, preconcentration, redissolution, etc.). The routine application of )uSEC-GC is a case in point. For quantitative analysis, most instruments require a solution. On-line combinations of sample treatment and analytical systems are being studied intensively. The idea behind such systems is to perform sample extraction, clean-up and concentration as an integral part of the analysis in a closed system [14]. 

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