Sample depth

Locational considerations include both surficial location and screened interval, ie, the sampling depth. The surficial location is selected based on whether the sample is to represent background quaUty or quaUty at the location of contamination, or potential leak location. In selecting the surficial location, the groundwater flow parameters, velocity and direction, are assumed to be known from other monitoring wells or borings already completed. 

Destructive Chemical bonding Depth profiling Quantification Accuracy Detection limits Sampling depth Lateral resolution Imaging/mapping... 

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... 

Electron spectroscopic techniques require vacuums of the order of 10 Pa for their operation. This requirement arises from the extreme surface-specificity of these techniques, mentioned above. With sampling depths of only a few atomic layers, and elemental sensitivities down to 10 atom layers (i. e., one atom of a particular element in 10 other atoms in an atomic layer), the techniques are clearly very sensitive to surface contamination, most of which comes from the residual gases in the vacuum system. According to gas kinetic theory, to have enough time to make a surface-analytical measurement on a surface that has just been prepared or exposed, before contamination from the gas phase interferes, the base pressure should be 10 Pa or lower, that is, in the region of ultrahigh vacuum (UHV). 

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... 

An infrared beam is directed through a crystal of refractive index (ni) onto a sample of smaller refractive index (n2). The intensity of the reflected beam is monitored as a function of the wavelength of the incident beam. These absorptions are used to identify the chemical structure. ATR has a sampling depth of about 0.3-3.0 microns. 

All application verification and soil samples must be individually labeled with unique sample identification (ID) and other identifying information such as study ID, test substance name, sample depth, replicate, subplot and date of collection, as appropriate. Proper study documentation requires that sample lists and labels be created prior to work commencing in the field. Water- and tear-resistant labels should be used since standard paper labels may become water-soaked and easily torn during sample handling. Sample lists should have the same information on them as the labels and are a convenient place to record plot randomization, initials of the individual who collected the sample, and date of collection. As such, the sample list is important in establishing chain of custody from the point of sample collection until its arrival at the laboratory. 

Of course, there is no point in overfilling your NMR tubes. This can make shimming more difficult (but certainly not impossible as in the case of too low a sample depth) but more importantly, it merely wastes materials and gives rise to unduly dilute samples giving reduced signal/noise. Any sample outside the receiver coils does not give rise to signal. 

Figure 2.1 Sample depth and magnetic field homogeneity.

An ESRI system can be built with small modifications of commercial spectrometers by, for example, gradient coils fixed on the poles of the spectrometer magnet, regulated direct current (DC) power supplies, and required computer connections [40,53,55]. Gradients can be applied in the three spatial dimensions, and a spectral dimension can be added by the method of stepped gradients. The spectral dimension is important when the spatial variation of ESR line shapes (as a function of sample depth) is of interest this situation will be described below, in the ESRI studies of heterophasic polymers. In most systems, the software for image reconstruction in ESRI experiments must be developed in-house. 

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