Sample preparation for trace element and residue analysis

2 Sample preparation for trace element and residue analysis 

The high sensitivity of modem instrumental techniques such as ICP-MS (Chapter 9) means that in many cases only small samples (typically, a hundred milligrams or less) need be taken for destructive analysis. However, this also means that the amounts of some individual elements may be very low, and problems of contamination can be significant. Common external contaminants include A1 from deodorants, Pb from paint or car exhausts, Zn from skin particles (and therefore from dust), and Na from sweat. The levels of contamination for each batch of samples will be revealed by the sample 

The matrix is the major component of the solution (or of the solid if using laser ablation or SEM). Matrix differences between standards and samples or between samples may result in differences of elemental sensitivity. Therefore, it is desirable that all the blanks, calibration standards, and samples have the same matrix (i.e., are matrix matched). This is relatively easy to achieve in solution, but can be a major problem with the analysis of solid samples. 

General inorganic trace element preparation methods 

The method used to dissolve samples may have an important impact on the quality of the data for some elements. Obviously, if the sample has not been fully dissolved, then quantification will give less than the true yield for some or all elements. Some individual elements may also form insoluble species or complexes during dissolution (e.g., Sn, Cr), and special precautions are necessary to ensure that such complexes are dissolved. Mercury in solution will often be absorbed onto the surface of glass vessels. Quantification will also be less than expected where volatile elements or their compounds are lost a process which may be aggravated if heating in an open vessel. 

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