Sampled depth analysis

Auger electron spectroscopy is the most frequently used surface, thin-film, or interface compositional analysis technique. This is because of its very versatile combination of attributes. It has surface specificity—a sampling depth that varies... 

A number of techniques are available for determining the composition of a solid surface. Since the surface plays an important role in many processes, such as oxidation, discoloration, wear, and adhesion, these techniques have gained importance. The choice of a surface analysis technique depends upon such important considerations as sampling depth, surface information, analysis environment, and sample suitability. Different... 

Mann, A.W., Birrell, R.D., Fedikow, M.A.F., de Souza, H.A.F. 2005. Vertical ionic migration mechanisms, soil anomalies, and sampling depth for mineral exploration. Geochemistry - Exploration, Environment, Analysis, 5, 201-210. 

Both LIBS and LA-ICP-MS offer spatial and depth resolution. A single laser shot provides an instantaneous measurement of approximately several nanograms to micrograms of sample. For spatial analysis, the laser is focused to several tens of microns and scanned across a surface. For depth analysis (including inclusions), the laser is pulsed repetitively at a single location to drill a channel into the sample (Fig. 5). 

Also, Petty et al. (2002) performed an in depth analysis of the OCP fraction of SPMD extracts by gas chromatography-mass spectrometry (GC-MS) resulting in the tentative identification of about 400 airborne organic chemicals, which were not present in SPMD field blanks. The OCP fraction represents only one of several enriched fractions from SPMD samples. Table 8.1 summarizes the various classes of compounds tentatively identified in SPMDs exposed to indoor air. 

Chemical differences in the Auger peaks are also present in the a-WCl a-W2C sample. Although the usual sputter profile does not give information about the distribution of chemical states in the sample, analysis of the W and C components suggests that besides the surface component, two different carbide components are present. The behaviour of the two bulk components of W and C is the same the first is located near the surface and decreases deeper into the sample the second increases to become the most important in the deeper part of the sample. RHEED analysis indicates a-WC but the depth sensitivity of this method is about 5-10 nm. XRD analysis indicates the presence of a-WC,a-W2C and W with a depth sensitivity of a few pm. Thus, the first bulk component of W and C can be identified as a-WC and the second as a-W2C. The overall sample consists of a contamination layer, followed by a thin layer of a-WC on top of the a-W2C phase. 

With very viscous or semi-solid liquids such as syrups, molasses and massecuite, the sample is taken by means of a cylindrical metal sampler in such a way that proportionate amounts are taken at different depths. With very dense products which may have crystallised sugar at the bottom, it is especially necessary to reach with the sampler the very bottom of the vessel. Several samples are withdrawn and mixed and the sample or samples for analysis (about 200 grams each) then stored in glass bottles with ground stoppers. 

Species distribution studies have shown that trace element (e.g. metals) concentrations in soils and sediments vary with physical location (e.g. depth below bed surface) and with particle size. In these speciation studies the total element content of each fraction was determined using a suitable trace element procedure, for example, solid sample analysis by X-ray emission spectroscopy or neutron activation analysis, or alternatively by dissolution of sample and analysis by ICPOES, AAS or ASV. The type of sample fraction analysed can vary, and a few... 

Two approaches are available. In the first a systematic survey is made of samples from a grid of say 50 m2 at a fixed depth of 50 cm (Fortunati et al., 1994). These samples are inspected and the appropriate parameters measured. The results of this preliminary study act as a guide to further sampling and analysis. With this type of systematic sampling plan the number of samples can easily become unmanageable and their study uneconomic. Furthermore, sampling at a fixed depth will not be useful where the site has been subject to landfill or, as is often the case on industrial sites, has been built up by deposits of fill material itself contaminated. 

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