Sampling segregation

Larger negative bias noted for higher sample concentrations due to poor sample solubility, resulting in sample segregation (precipitation) after collection as the solution temperature drops from 37°C to ambient (or refrigerated) conditions for analysis. 

The purpose of trip blanks is to assess the collected sample representativeness by determining whether contaminants have been introduced into the samples while they were handled in the field and in transit, i.e. in coolers with ice transported from the site to the analytical laboratory. A possible mechanism of such contamination is the ability of some volatile compounds, such as methylene chloride or chlorofluor-ocarbons (Freons), to penetrate the PTFE-lined septum and dissolve in water. Potential sources of this type of contamination are either ambient volatile contaminants or the VOCs that could be emanating from the samples themselves, causing sample cross-contamination. To eliminate ambient contamination, samples must not be exposed to atmospheres containing organic vapors. Cross-contamination is best controlled by such QA measures as sample segregation and proper packaging. 

Table 11 Sample segregation between classes of dangerous goods. .. 85...

TABLE II. SAMPLE SEGREGATION BETWEEN CLASSES OE DANGEROUS GOODS (Taken from the IMDG-Code [10])... 

For 3 to 33% Sc the sample segregates macroscopically into the black and golden phases. 

Fluid samples will be taken using downhole sample bombs or the MDT tool in selected development wells to confirm the PVT properties assumed in the development plan, and to check for areal and vertical variations in the reservoir. In long hydrocarbon columns (say 1000 ft) it is common to observe vertical variation of fluid properties due to gravity segregation. 

The measuren.cnts are performed on a sample made from Inconell IN 718 placed at our disposal by Me oren- und Turbinen-Union Miinchen GmbH (MTU). The sample is of disk shape and has a curved side and a flat side, see also fig. 6. On the curved side MTU had detected a segregation reaching to the surface but with unknown depth. It had been detected by segregation etching and its existence was confirmed by eddy current testing. Both methods are successful only in such a special case where the segregation extends to the surface. 

Figure 7 IN718 sample with segregation, SQUID-Signal versus rotation angle, scan radius is constant and equal to radial coordinate of segregation. Measurements are performed after demagnetization.

Figure 6 Sketch of sample from IN718 containing segregation, placed in measurement system.

When the target population is segregated, or stratified, equation 7.5 provides a poor estimate of the amount of sample needed to achieve a desired relative standard deviation for sampling. A more appropriate relationship, which can be applied to both segregated and nonsegregated samples, has been proposed. ... 

Temperature-risiag elution fractionation (tref) is a technique for obtaining fractions based on short-chain branch content versus molecular weight (96). On account of the more than four days of sample preparation required, stepwise isothermal segregation (97) and solvated thermal analysis fractionation (98) techniques usiag variatioas of differeatial scanning calorimetry (dsc) techniques have been developed. 

Generally, Httle is known in advance concerning the degree of homogeneity of most sampled systems. Uniformity, rarely constant throughout bulk systems, is often nonrandom. During the production of thousands of tons of material, size and shape distribution, surface and bulk composition, density, moisture, etc, can vary. Thus, in any bulk container, the product may be stratified into zones of variable properties. In gas and Hquid systems, particulates segregate and concentrate in specific locations in the container as the result of sedimentation (qv) or flotation (qv) processes. 

Whenever possible a powder should be sampled when in motion and the whole of the stream of powder should be taken for many short increments of time in preference to part of the stream being taken for the whole of the time. Observance of these rules coupled with an understanding of the manner in which segregation takes place leads to the best sampling procedure. Care and skill in abstracting samples is needed and cannot be overemphasized. 

Stored Free-Flowing Material. It is practicahy impossible to representatively sample stationary free-flowing powder because of the severe segregation that has almost certainly occurred. If there is no alternative but to sample this material, several samples should be taken and analyzed separately, so that an estimate can be made of the rehabhity of the measured parameter. For free-flowing materials stored in small hoppers, dmms, cans, boxes, and... 

Figure 7 Quantitative high depth resolution profile of the major elements in the thin-film structure of Al /TIN /Si, comparing the annealed and unannealad structures to determine the extent of interdiffusion of the layers. The depth profile of the unannealed sample shows excellent depth resolution (a). The small amount of Si in the Al is segregated toward the Al/TiN interface. After annealing, significant Ti has diffused into the Al layer and Al into the TIN layer, but essentially no Al has diffused into the Si (b). The Si has become very strongly localized at the Al / TIN interface.

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