Depth profiling studies, mineral

SIMS has become one of the most important tools for the characterization of experimental products because of its minimal sample requirements, high spatial resolution, excellent sensitivity, and unsurpassed ability for depth-profile measurements. Most of the experimental work can be split into two different areas. The first consists of studies examining diffusion rates of different elements in minerals or melts under a variety of pressure, temperature, and fluid conditions, typically by using an isotopically enriched tracer. These analyses are done either by cutting a surface parallel to the diffusion direction and taking a traverse of spot analyses (for conditions in which profiles in the tens to hundreds of micrometers are expected) or by depth-profiling in from the mineral surface to depths of as much as 5-10 micrometers. In the latter mode, depth resolution on the tens of nanometer scale is possible (see Chapter 4). The second area is focused on determining partition coefficients for trace elements between different minerals and fluids/melts at specific temperatures, pressures, and fluid conditions, to provide the data needed to interpret trace element contents measured in natural minerals. This type of analysis typically involves spot analysis of mineral run products. 

Detailed studies of mantle xenoliths combining age determinations with the results of mineral barometry allow age-depth profiles to be constructed for some kimberlite pipes (Fig. 3.11). The results of such studies do not show any obvious age-depth relationship which is puzzling, maybe reflecting melt infiltration... 

In dmg discovery, preliminary PK studies are usually conducted in rodents to evaluate the extent of dmg exposure in vivo. This is commonly followed by PK studies in larger animals such as dog or monkey to better characterize the PK profile of the compound and to support safety studies. Pharmacokinetic scaling (also called allometry) is a discipline that is used to predict human PK profiles using preclinical data and is widely used in predicting the dmg human half-life, dose, and extent of absorption. Accurate prediction of a human PK profile is imperative to minimize dmg failure in development due to poor PK attributes. A detailed description of methods in predicting human PK is beyond the scope of this chapter but can be found in many excellent reviews (Obach et al., 1997 Miners et al., 2004 Poggesi, 2004 Raunio et al., 2004 Thomas et al., 2006 Hurst et al., 2007). A more in-depth discussion of various PK concepts and their applications can be found in various references (Gibaldi and Perrier, 1982 Rowland and Tozer, 1995 Hurst et al., 2007). 

Numerous studies have also observed the humification index (HIXem) decreasing with depth in the soil profile. Bu et al. (2010) found a noticeable decrease in all four soil types. Corvasce et al. (2006) and Hassouna et al. (2010) made similar observations to those of Cannavo et al. (2004) showing a decrease in aromaticity correlating to the decrease in HIXem. This decrease has been hypothesized to indicate that larger, more humified molecules are retained on mineral surfaces and the smaller, more mobile molecules can be transported to deeper soil layers. In a smdy on the affect of acidification on soil DOM, Ohno et al. (2007) also observed a decrease in HIXem with depth. They found that the decrease in HIXem with depth was much more pronounced in soil samples in deciduous than coniferous forests. In addition, in both forest types samples from an acidified watershed had higher HIXem values than samples from the reference watershed. 

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