Trace element analytical precision

The abundance of a trace element is often too small to be accurately quantihed using conventional analytical methods such as ion chromatography or mass spectrometry. It is possible, however, to precisely determine very low concentrations of a constituent by measuring its radioactive decay properties. In order to understand how U-Th series radionuclides can provide such low-level tracer information, a brief review of the basic principles of radioactive decay and the application of these radionuclides as geochronological tools is useful. " The U-Th decay series together consist of 36 radionuclides that are isotopes (same atomic number, Z, different atomic mass, M) of 10 distinct elements (Figure 1). Some of these are very short-lived (tj j 1 -nd are thus not directly useful as marine tracers. It is the other radioisotopes with half-lives greater than 1 day that are most useful and are the focus of this chapter. 

The second source of partitioning data is experimental equilibration of crystals and liquids followed by microbeam analysis of quenched run products. Starting materials can be natural rocks, or synthetic analogues. In either case it is customary to dope the starting material with the U-series element(s) of interest, in order to enhance analytical precision. Of course, doping levels should not be so high as to trigger trace phase saturation (e g.. 

Vandecasteele et al. [745] studied signal suppression in ICP-MS of beryllium, aluminium, zinc, rubidium, indium, and lead in multielement solutions, and in the presence of increasing amounts of sodium chloride (up to 9 g/1). The suppression effects were the same for all of the analyte elements under consideration, and it was therefore possible to use one particular element, 115indium, as an internal standard to correct for the suppressive matrix effect, which significantly improved experimental precision. To study the causes of matrix effect, 0.154 M solutions of ammonium chloride, sodium chloride, and caesium chloride were compared. Ammonium chloride exhibited the least suppressive effect, and caesium chloride the most. The results had implications for trace element determinations in seawater (35 g sodium chloride per litre). 

Precision studies should mirror the operating conditions used during routine use of the method. For example, the range of operating conditions, such as the variation in the laboratory temperature, needs to reflect that which will occur in practice. In addition the same number of replicate measurements per test portion should be used. Where a range of analytes is measured by a single method (e.g. pesticides by GC or trace elements by ICP-MS), or where different matrix types are encountered, it is necessary to determine the precision parameters... 

Effect of Coal Particle Size on Analytical Precision of Trace Elements... 

Preliminary studies have shown that it is possible to remove over half of the potentially toxic trace elements present in coal when the mineral matter is reduced by coal washing. When coal is burned in a power plant, about 13% of the mercury and about 50% of the lead and cadmium may remain with the fly ash. Analytical chemical techniques have been developed to determine Hg, Cu, Cr, Mn, Ni, Cd, Pb, and F in coal and fly ash. These techniques produce accurate and precise results despite the fact that there are no coals with established trace element content, except for mercury. 

Another problem encountered when analyzing coal for trace elements is the lack of standards. Except for mercury, there is no certified standard coal presently available for use in trace element analysis. Because the precision and accuracy of the analytical procedures used are in many cases affected by the matrix one is dealing with, the lack of a standard coal is a serious problem. 

More than seven replicates may be analyzed however, all of the obtained results must be used in the calculation, unless there is a well-justified reason to discard any of them. MDLs are specific to a given matrix, method, and instrument, and greatly depend on the analyst s technique. The better the analytical precision, the lower the calculated value of the MDL. Laboratories are required to perform MDL studies at least once a year (APHA, 1998 EPA, 1999d). However, the MDLs may be determined more often if there is a change in the laboratory extraction, analysis, or instrumentation. For trace element analyses, the MDL studies are performed in reagent water only, as a metal-free solid matrix that would successfully emulate natural soils does not exist. 

Determines analytical precision of a sample One for every 10 samples for trace element... 

Laboratories subsample two aliquots of a field sample from the same container and treat them as two separate samples. Typically, laboratory duplicates are prepared and analyzed with every 10 samples in trace element and inorganic analyses. This allows laboratories to calculate the RPD between the two results as a measure of analytical precision. Laboratory duplicates are rarely used in organic compound analysis. 

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