Sample layer thickness

Figure 3.1.6. The variation of T (x, t)° C atx = 0 as a function of sample layer thickness, for three layer thicknesses I of 0.1 mm, 0.25 mm, and 0.5 mm. The dotted line shows the temperature of the heating element.

Values for Sample, Layer Thickness, Surface Area, Wattage, and Density Gradient in Several Types of Stationary Density Gradient... 

Reference Sample layer thickness (mm) V/cm area (cm2) Conductivity (mmho/cm) Ampere (x 10s) W/cms (x 10s) Cooling Density gradient (g/cm4)(x 104)... 

Fig. 27 Determination of the diffusion coefficient of partially per-deuterated methanol into a water (D2O) swollen PNIPAAm gel at 21 °C. The increase of magnetisation of a thin sample layer (thickness about 100 pm) is measured. The layer is located at a distance of 4.8 mm from the sample surface...

For detection of defect dimensions defectometers were used made of examined sample material allowing to reveal defects of 0.25-1% x-rayed steel layer thickness in range of 100-500mm thickness at 11 MeV. 

Though a powerfiil technique, Neutron Reflectivity has a number of drawbacks. Two are experimental the necessity to go to a neutron source and, because of the extreme grazing angles, a requirement that the sample be optically flat over at least a 5-cm diameter. Two drawbacks are concerned with data interpretation the reflec-tivity-versus-angle data does not directly give a a depth profile this must be obtained by calculation for an assumed model where layer thickness and interface width are parameters (cf., XRF and VASE determination of film thicknesses. Chapters 6 and 7). The second problem is that roughness at an interface produces the same effect on specular reflection as true interdiffiision. 

A layer of condensed eluent is built up ahead of the evaporation site which acts as a thick layer of retaining stationary phase, thus blocking the further movement of all but the most volatile compounds into the column. Solvent evaporation, therefore proceeds from the rear towards the front of the sample layer (see Eigure 2.2). 

Figure 23 Distribution of average layer thickness within a sample in dependence on melt temperature T , and shear rate y by injection molding.

Fig. 8. Residual impression depth against reciprocal long period for two series of lamellar PE samples with surface layer thicknesses of 80 (O) and 200 A (A) respectively5Sa)...

The interfaces here also have contribution to the hardness. For Samples 3 and 4, there are no obvious interfaces between Layers A and B because the individual layer thickness is so thin that it is hard to form sharp interfaces. It is more like a mixed structure according to the process. For Sample 5, the interfaces are possibly formed due to the increase of Layer A. So the hardness of Samples 3 and 4 is still much lower than monolayer A, but the hardness of Sample 5 is close to the monolayer A. 

Here, Q is the heat energy input per area p and Cp are the density and specific heat capacity, respectively and indices g, d, and s refer to the gas, metal, and liquid sample layers, respectively. With Eq. (106), the thermal conductivity of the sample liquid is obtained from the measured temperature response of the metal without knowing the thermal conductivity of the metal disk and the thickness of the sample liquid. There is no constant characteristic of the apparatus used. Thus, absolute measurement of thermal conductivity is possible, and the thermal conductivities of molten sodium and potassium nitrates have been measured. ... 

Plates with 0.5- to 2-mm layer thickness are normally nsed for increased loading capacity. Layers can be self-made in the laboratory, or commercially precoated preparative plates are available with silica gel, alumina, cellulose, C-2 or C-18 bonded siliea gel, and other sorbents. Resolution is lower than on thinner analytical layers having a smaller average partiele size and particle size range. Precoated plates with a preadsorbent or eoneentrating zone faeilitate application of sample bands. 

The main differences between TLC and PLC are due to the layer thickness and particle size of the stationary phase and the amount of sample applied to the plate. 

Single linear developments are mostly employed in the vertical mode. The apph-cabihty of the horizontal mode is discussed in Chapter 6. For circular and anticircular developments, the movement of the mobile phase is two-dimensional however, from the standpoint of sample separation it is a one-dimensional technique. Circular developments result in higher hRp values compared to linear ones imder the same conditions, and compoimds are better resolved in the lower-AR range. The same effect is noticed on plates with a layer thickness gradient (see Section 5.2.1). On the other hand, using antieircular developments, compounds are bettCT resolved in the upper-M range. 

PLC is used for separations of 2 to 5 mg of sample on thin-layer chromatography (TLC) plates (0.25-nun layer thickness) or high-performance TLC (HPTLC) plates (0.1-mm thickness). In these instances, the method is termed micropreparative TLC. The isolation of one to five compounds in amounts ranging from 5 to 1000 mg is carried out on thicker layers. PLC is performed for isolation of compounds to be used in other tasks, i.e., further identification by various analytical methods, such as ultraviolet (UV) solution spectrometry [1] or gas chromatography/mass spectrometry (GC/MS) [2], obtaining analytical standards, or investigations of chemical or biological properties [3]. 

The amoimt of lipid applied to the plate varies depending on the ease of separation of individual lipid components in the sample. Usually 25 to 50 mg of the neutral lipid sample can be applied to a 20 X 20 cm preparative plate with the silica gel G layer thickness of 0.5 mm, whereas only about 4 mg of phospholipids can be applied on these plates. 

Since natural Au consists solely of Au, the interface-selective enrichment technique cannot be applied in Au studies. The absorber thickness for Au is required to be large and therefore multilayered samples of Au layers/3r/ metal layers have to be prepared. The spectra for Au/Fe with varying Au-layer thickness are shown in Fig. 7.83 [437]. The results were interpreted as follows large magnetic hyperfine fields at Au sites exist only within two monolayers at the interface region, which are supposed to be induced by direct coupling with anti-ferromagnetically oriented Fe 3d atoms. 

The principal difference between analytical TLC and preparative TLC is one of scale and not of procedure or method. Scale up is achieved by increasing the thickness of the layer and the length of the edge of the plate to which the sample is. applied. Preparative TLC plates range in size from 20 x 20 cm to 20 X 100 cm and are coated with a sorbent layer 0.5 to 10.0 as thick. The most commonly used layer thicknesses are 1.0 and 2.0 mm. Analytical layers are suitable for micropreparative applications and when high resolution is required. In general, the loading capacity increases with the square root of the layer thickness but the resolution is usually less for thicker layers. 

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