Sample preparation geology

The Benefits of the X Series 2 ICP-MS for the Analysis of Geological Samples Prepared Using the Lithium Metaborate Fusion Method, Thermo Scientific Application Note—40790, 2007, http //www.thermo.com/eThermo/CMA/PDFs/Articles/articles-File 2375.pdf. 

Direct sampling of solids may be carried out using laser ablation. In this technique a high-power laser, usually a pulsed Nd-YAG laser, is used to vaporize the solid, which is then swept into the plasma for ionization. Besides not requiring dissolution or other chemistry to be performed on the sample, laser ablation ICPMS (LA-ICPMS) allows spatial resolution of 20-50 pm. Depth resolution is 1-10 pm per pulse. This aspect gives LA-ICPMS unique dit nostic capabilities for geologic samples, surface features, and other inhomogeneous samples. In addition minimal, or no, sample preparation is required. 

Laser ablation ICP-MS (LA-ICP-MS) was established in the early 1990s as a potential routine tool for the measurement of trace and ultra-trace elements in silicate systems for geology. Early studies (Perkins et al. 1993) used sample preparation techniques identical to that used to prepare rock samples for WDXRF, i.e., either a pressed powder disk or a glass bead fusion method (see Appendix VIII). Such studies concluded that LA-ICP-MS had the potential to surpass XRF in terms of the limits of detection achieved and INAA in terms of the speed of analysis (Perkins et al. 1993 481). It has long been recognized that the main limit on the quantitative performance of LA-ICP-MS is the homogeneity at the trace and ultra-trace level of the solid calibration standards available. Subsequent work (e.g., Hollecher and Ruiz 1995, Norman et al. 1996) has demonstrated that some of the international... 

To convert geologic samples to a suitable form for analysis, many different chemical preparation techniques must be used. These diverse techniques all have one general feature in common any preparation procedure providing a yield of less than 100% may produce a reaction product that is isotopically different from the original specimen because the different isotopic species have different reaction rates. 

Two types of coal ash samples have been prepared routinely for analysis at the Illinois Geological Survey. Low-temperature ash samples (12), in which the bulk of the mineral matter remains unchanged, are prepared by reaction of the coal with activated oxygen in a radiofrequency field. The effective temperature produced by this device is approximately 150 °C. Such samples were unsatisfactory for emission spectroscopic analysis. It is postulated that the presence of largely unaltered mineral matter, such as carbonates, sulfides, and hemihydrated sulfates (12), caused the observed nonreproducibility of results. High-temperature ash samples, prepared in a muffle furnace, consisted mainly... 

Brick and tile samples from buildings including the Chapel at St. Maiy s City and sites in Virginia were prepared and analyzed by INAA as part of an earlier study (12). These data have been combined with new results from further geologic sampling at the site. 

X-ray fluorescence is a rapid and low-cost method that can be performed on solid samples. However, the depth of penetration of X-rays in most solid samples is relatively shallow. High-precision XRF on geological samples such as obsidian requires preparation of homogeneous, powdered samples pressed into pellet form. If some loss of precision and accuracy due to irregular size, shape, and thickness of samples is acceptable, obsidian specimens can be analyzed non-destructively. Samples smaller than 1 cm in diameter or with element concentrations less than 5 ppm are generally not suitable for XRF. XRF can determine about 10-15 elements in obsidian (K, Ti, Mn, Fe, Zn, Ga, Rb, Sr, Y, Zr, Nb, Pb, and Th). Fortunately, many of the measurable elements are the incompatible elements which provide discrimination between sources. 

Geological samples were collected from primary sources and secondary deposits of obsidian. In most cases, the geographic coordinates of source samples were also recorded. The geological samples were shipped to MURR for sample preparation and analysis. 

Geological and biological sample preparation for subsequent analysis often involves digestion in highly oxidant media such as nitric or perchloric acid. This is a frequent... 

LAB / Laboratory for sample preparation (soil and sediment samples). Geological Survey of the Slovak Republic. 

Sample Preparation. Herrin No.6 (Illinois No.6) and Indiana No.5 (Illinois No.5) coals obtained from the Illinois Geological Survey Sample Bank were used in this study. The whole coals were split into four fractions each of which was placed in a sealed, 5-gallon drum. The fourth fraction was ground to minus 200 mesh and then introduced into a nitrogen gas powered (100 psi) Sturtevant fluid energy mill. In this device the coal particle size is reduced to the micron level by impaction between coal particles themselves and with the impaction chamber walls. Proximate and elemental data for these micronized coals are reported in Table I. 

Trace element measurements by ICP-MS have been used for geological exploration [292]. The use of ICP-MS for measurement of precious metals in rocks has been recently reviewed [293]. Typically sample preparation includes extraction and concentration of precious metals and separations from potentially interfering elements [293]. For example, HfO+ of masses 194, 195, and 196 overlaps with Pt+ isotopes. Limits on dissolved solid concentrations to about 0.2% also limit the detection of small quantities of precious metals in the solid. 

Oxide materials are distinguished by the fact that the compound forms of the elements may be very different, depending on the many geological types. In general, various main components (greater than 10 weight percent) and trace concentrations (less than 0.01 weight percent) are present. The analysis must take this into account not only in the sample preparation (preparation of solutions) but also in the desired indication of results. 

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