High-precision trace element

High-Precision Trace Element and Organic Constituent Analysis of Oil Shale and Solvent-Refined Coal Materials... 

Jetuicr G.J., Longerich H.P., Jackson S.E. and Fryer B.J., 1990, ICP-MS a powerful tool for high precision trace-element analysis in earth sciences evidence from analysis of selected U.S.G.S. reference samples. CA w. Geol., 83, 133-148. 

Trace elements include heavy metals, some of which have recently received particular attention. Many definitions of heavy metals have been put forward. The simplest and most precise describes heavy metals as all metal compounds of atomic weight over 20. Other definitions are based on the specific weight, and give the lower limits for heavy metals as 4.5, 5, or even 6 g per cm. Due to toxicity of some heavy metals and the possibility of environmental contamination, the potential for high risk is linked to Hg, Cd, As, Pb, as well as Cu, Zn, Sn, Cr, Ni. 

Chapters 7 and 8 describe two major techniques for the monitoring of trace elements in environmental samples atomic absorption (AA) and inductively coupled plasma-atomic emission spectroscopy (ICP). AA is most ideally suited for analyses where a limited number of trace metal concentrations are needed with high accuracy and precision. ICP has the advantage of multielement analysis with high speed. 

As discussed above, ICP-IDMS is becoming a highly valuable method for trace element and element-speciation analysis. For ICP-IDMS the highly precise and accurate isotope ratio measurements that are currently required can be made by resorting to multicollector-ICP-MS. 

In the photographic procedure, the lack of a suitable internal standard for exposure correction, the attempt to record and determine all elements on one generalized exposure, and the very high concentration of the trace elements in the ash (for some samples as much as 33 times the amount reported in the coal) caused a poor relative standard deviation. However, of the 13 elements determined, only Co, Ni, Cr, and V were less precise than 20%, a level which we feel is suitable for a photographic method. 

XRF offers a unique approach for rapid, non-destructive elemental analysis of liquids, powders, and solids. Although the first row transition elements are the most sensitive, elements from atomic number 12 (magnesium) and greater can be measured over a dynamic range from trace (ppm) to major (percent) element concentrations. EDXRF is well suited for qualitative elemental identification of unique samples, while WDXRF excels at high precision quantitative analysis. 

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