Sample at depth

The large areal variation in environmental TCDD concentrations is confirmed by the analytical data resulting from using the four different methods to obtain samples at depth. An examination of Figure 3 which presents road centerline data from two 15-foot segments shows variations in the upper six inches ranging, from 295 to 895 and from 2.1 to 1020. 

Organic materials may be absorbed from the surface film or surface waters, then desorbed into the water samples at depth, thereby smearing the real vertical distributions. 

If contamination is the reason for sampling, samples at depth along the transect line will also be required. Depending on the soil depth, depth to the water table, the severity of contamination, and the type of soil, deep samples may need to be taken at each location. As with the transect, depth samples must be taken until the contaminant or analyte of interest is found to be at background levels. Thus, several depths may need to be taken at each location along the transect. 

Consequently, for an accurate quantification of surfactants in the water column, sampling must be performed by taking surface microlayer samples (at depths between 0 and 3—5 mm), using a surface sampler, and at various greater depths with Ruttner or similar bottles. 

Soil core data are available for only six of the pesticides discussed in this paper. The six pesticides are aldlcarb atrazlne 1,2-dibromo-3-chloropropane (DBCP) 1,2-dlchloropro-pane (DCP) 1,2-dlbromoethane (EDB) and slmazlne. Cores were always sampled at depths greater than one meter and the soil was characterized physically and chemically. The importance of soil core sampling in pesticide leaching assessments is presented in the Discussion section. 

The study of sulfide metabolism at hydrothermal vents dictated the development of methods that could process hundreds of samples which contain complex mixtures of sulfur compounds in a variety of blood, seawater and tissues samples. In addition, we needed the capability of using "S-radiolabeled compounds for the tracing of complex sulfur metabolic pathways in bacteria and animal compartments of the different hydrothermal vent symbioses. In some instances, in situ sampling by submersibles at depths of 2500 meters with associated recovery times of two hours necessitated the remote derivatization of samples at depth prior to recovery. None of the above methods completely met our needs. We have adapted the bimane-HPLC method (24.351 for shipboard use and have found it a particularly robust method for studying a number of questions concerning the role of reduced sulfur compounds in the marine environment. 

In addition to using X-rays to irradiate a surface, ultraviolet light may be used as the source for photoelectron spectroscopy (PES). This technique, known as ultraviolet photoelectron spectroscopy (UPS, Figure 7.38), is usually carried out using two He lines (Hel at 21.2 eV and Hell at 40.8 eV), or a synchrotron source. This technique is often referred to as soft PES, since the low photon energy is not sufficient to excite the inner-shell electrons, but rather results in photoelectron emission from valence band electrons - useful to characterize surface species based on their bonding motifs. It should be noted that both UPS and XPS are often performed in tandem with an Ar" " source, allowing for chemical analysis of the sample at depths of < 1 J,m below the surface. 

Jingbian is located in the central part of the Ordos Basin, where the oil and gas potential has long been considered to be poor because favourable structures are not evident in the seismic data. In 1988, however, the Changqing Oil Company proposed a scientific research well. This was preceded by a surface gas geochemical survey along several traverses, one of which passed through the site of the proposed well. The surface material, which is mainly aeolian sand, dry river-bank sediments and loess, was sampled at depths of 2-3 m at intervals of one km along traverse lines. At each sample site, Hg in... 

Suppose a beam of cross-sectional area A falls on a sheet sample of thickness t in the symmetrical reflection geometry, as in Figure 2.24a. We assume, for the sake of simplicity, that the rays in the beam are all parallel to each other. Now consider a layer of thickness dx inside the sample, at depth x below the flat surface, where the irradiated volume is equal to dx A/ sin 0. Before reaching this depth the beam has traveled distance Z within the sample, where l is equal to x/sin 0, and has suffered attenuation by a factor exp(—/x/), p being the linear absorption coefficient. The scattered beam must travel the same distance within the sample again on its way out. If i 20) is the intensity of scattering per unit volume of the sample, then the contribution dl(20) to the total scattering intensity by the layer dx at depth x is... 

Table 1. Monterey Miocene Formation samples, shown in Figs. 4 and 5 (a) sulfur percent, S/C ratio and Rock Eval for kerogens and oils, see also description in Figs. 4 and 5 (b) the same data on core samples at depth 1155-2490 m...

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