Sample spreading

The introduction of the sample valve, however, helped establish radial equilibrium early in the separation but, unless some special sample spreading device is employed at the front of the column, equilibrium will not necessarily occur at the point of injection. The stream splitting process is depicted in Figure 2. 

In the powder diffraction technique, a monochromatic (single-frequency) beam of x-rays is directed at a powdered sample spread on a support, and the diffraction intensity is measured as the detector is moved to different angles (Fig. 1). The pattern obtained is characteristic of the material in the sample, and it can be identified by comparison with a database of patterns. In effect, powder x-ray diffraction takes a fingerprint of the sample. It can also be used to identify the size and shape of the unit cell by measuring the spacing of the lines in the diffraction pattern. The central equation for analyzing the results of a powder diffraction experiment is the Bragg equation... 

Filter thru a tared sintered glass crucible, wash the residue with warm distd w until the disappearance of yel color(ca 100ml in small portions) and dry in an oven to const wt DjParticle Size. Shake(by hand, or mechanically) a lOOg sample spread on a tared No 10 US Std sieve, which is placed on top of a tared No 100 sieve and determine the amt of material retained on each sieve. The method is described in detail in US Federal Specification P-S-536... 

Briefly, the moisture is detd by heating a lg sample, spread on the bottom of a capsule,... 

In the powder diffraction technique, a monochromatic (single-frequency) beam of x-rays is directed at a powdered sample spread on a support, and the diffraction intensity is measured as the detector is moved to different angles (Fig. 4). The pattern obtained is characteristic of the material in the sample, and it can... 

The same authors 369,3701 also obtained similar results if the liquid crystal solvent was aligned by flow during the polymerization. They showed that the polymerization conditions lead to alignment of the fibrils within the polymer mass and of the chains within the fibrils polymers produced in this way could also be doped to a conductivity of 104 S cm-1 371). The morphology of polyacetylene produced by polymerization in a liquid crystal solvent, aligned both magnetically and by flow, has been studied by Montaner et al. 371). They show that the polymer film is made up of very long fibrils built from microfibrils. In one fibril, the orientation of microcrystalline domains with respect to the fibril axis is very well defined, whilst the orientation of the different fibrils in the sample spreads over 20°. 

Most dry reagent chemistries are designed to be self-contained analytical devices. Each element may have several functional zones that are introduced as single layers or combined into one layer during construction. Regardless of the number of layers present, all dry reagent elements have a support function, a reflectance function, and an analytical function (Fig. I). Some elements may also contain a sample-spreading function. 

Where present, the sole purpose of a sample spreading function is rapid lateral spreading of a sample after application (5). This feature mediates a uniform sample volume per unit volume of the element (Fig. 2). Substances commonly used to construct spreading functions include fabrics, membranes, and paper. 

Figure 1 Illustrates the experimental procedure used In making spreading resistance measurements. Two probes are carefully aligned and then stepped across the bevelled surface of a semiconductor sample at each point, the probes are lowered onto the sample surface and the resistance between the two probes Is measured and plotted. The technique Is referred to as the spreading resistance technique because the dominant resistance of a point contact diode occurs In a very small volume beneath the probe, where the current rapidly spreads out Into the sample. Spreading resistance profiles are usually computer-processed to yield resistivity or dopant concentration profiles.

The source sampling can be carried out either when the source is stationary or when it is mobile. Stationary sources are of four types (1) steady and uniform, (2) steady but not uniform, (3) unsteady but uniform, and (4) unsteady and nonuniform. The first type requires only one sample the second requires composite sampling at several location the third demands one sample spread over the entire operation and the last type calls for a composite and repeated sampling. 

The HILIC functional principle can be described as follows. On polar phases, polar molecules have retention when solvents that are more nonpolar than the stationary phase and that can be mixed with water are used. A layer of water develops on the phases surface. The polar sample spreads between this layer of water and the mobile phase. 

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