Geochemistry sample preparation

The chemistry of rare earth elements makes them particularly useful in studies of marine geochemistry [637]. But the determination of rare earths in seawater at ultratrace levels has always been a difficult task. Of the various methods applied, instrumental neutron activation analysis and isotope dilution mass spectrometry were the main techniques used for the determination of rare earths in seawater. However, sample preparation is tedious and large amounts of water are required in neutron activation analysis. In addition, the method can only offer relatively low sample throughputs and some rare earths cannot be determined. The main drawbacks of isotopic dilution mass spectrometry are that it is time-consuming and expensive, and monoisotopic elements cannot be determined as well. 

The study of obsidian by NAA has proved to be particularly fruitful because of the relatively limited number of sources and the extent to which it was traded (Beardsley et al. 1996, Cook 1995, Darling and Hayashida 1995, Kuzmin et al. 2002, Leach 1996). Studies have also extended to include other volcanic materials such as pumice (Bichler et al. 1997, Peltz et al. 1999). NAA has also been used for the analysis of flint as OES is insensitive and not reproducible due to the effect of the high silica content, and AAS requires significant sample preparation (Aspinall and Feather 1972). The wide range of appropriate materials extends to organic materials such as human bone (Farnum et al. 1995), and its exceptional sensitivity to trace elements has led to its wide use in geochemistry (for example in determining trace [ppb] contaminants in waters) and more recently in forensic chemistry. 

Figure 9 gives a brief overview of the sample preparation procedure used in onr laboratory. One point of note is that drying is carried out at 40 °C, instead of the 80-KX) C that is normal in many laboratories. Experience from organic geochemistry indicates that the lower temperature is preferable to ensure that no volatile components are lost before analysis. Splits from the dry, powdered sample are also used for carbon isotopic analysis and RockEval pyrolysis (Talbot Livingstone, 1989 Talbot Laerdal, 2000 Fig. 9), in fact it is our practice to perform the analysis first, as %N data from the elemental analyser allows us to estimate how much sample needs to be weighed for the N-isotope determination. As little as 100 /xg N are required for analysis. 

A wide range of analytical techniques are routinely employed in the geochemistry laboratory, and the sample preparation techniques required vary depending on the nature of the material, the type of analysis to be performed and the purpose of the study. In most cases some form of mechanical processing is required. A typical process for preparing solid rock samples for analysis is given below ... 

XRF is widely used for elemental analysis in geochemistry, archaeology, forensic science, and life sciences. The method has the advantages of simple analytical procedure as well as being non-destructive with a relatively short testing time. As with any analytical procedure, the analytical procedure for EDXRF includes sample preparation, sample measurement, and data treatment. 

Kane JS (1992) Reference samples for use in analytical geochemistry their availability, preparation, and appropriate use. Joum Geochem Explor 44 37-63. 

Data preparation began by excluding any possibly unreliable and irrelevant data from the set of 33 elements. The heavy mineral solution could have imparted excess sodium (Na) and was thus ignored. The mortar and pestle used could have contaminated the aluminum (Al). Based on the hardness of the material and relative contribution to the sample this is likely not a significant problem however the role of Al was monitored closely during the data analysis. Previous literature on the geochemistry of specularite (10, 11) and preliminary... 

Soil samples are usually collected at the surface proper or at depths of up to several metres below the surface. As far as possible, samples are kept in their original condition until they are prepared for analysis in the laboratory. The analytical procedures are invariably partial extraction techniques. This approach has been widely used in other branches of exploration geochemistry, but assumes particular importance in gas geochemical surveys for petroleum. 

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