Rotational sampling

Mechanical methods also exist for dividing up particulate material into suitably sized samples. Samples obtained by these means are usually representative of the bulk material within limits of less than 1 per cent, and are based upon the requirements established by the British Standards Institution. Sample dividers exist with capacities of up to 10 L and operate either by means of a series of rapidly rotating sample jars under the outlet of a loading funnel, or by a rotary cascade from which the samples are fed into a series of separate compartments. Sample dividers can lead to a great deal of time-saving in laboratories dealing with bulk quantities of powders or minerals. 

Fig. 1. Plot of the orientations of director and spinning axis of a rotating sample w.r.t. the external magnetic field.

Figure 2. Continued, b, With rotatable sample holder.

Raman often is evaluated as an alternative to an existing high performance liquid chromatography (HPLC) method because of its potential to be noninvasive, fast, simple to perform, and solvent-free. Raman was compared to HPLC for the determination of ticlopidine-hydrochloride (TCL) [43], risperidone [44] in film-coated tablets, and medroxyprogesterone acetate (MPA) in 150-mg/mL suspensions (DepoProvera, Pfizer) [45] it was found to have numerous advantages and performance suitable to replace HPLC. In an off-line laboratory study, the relative standard deviation of the measurement of the composition of powder mixtures of two sulfonamides, sulfathiazole and sulfanilamide, was reduced from 10-20% to less than 4% by employing a reusable, easily prepared rotating sample cell [46]. 

For the in situ Raman studies the Mo03/Si02 samples were pressed into wafers at 21 MPa. The pressed wafers were placed in a rotatable sample holder that was enclosed in a quartz cell equipped with an oven. The samples were oxidized at 773 K for 1 hour in O2 to minimize sample fluorescence, then were cooled to 343 K in flowing helium. The adsorbates were introduced through an injection port of the cell at 343 K with flowing helium, and the spectra were recorded at the same tenq>erature. 

The dynamic RIS model, which was proposed before to investigate the dynamics of local conformational transitions in polymers, is elaborated to formulate the increase in the number of excimer-forming sites through rotational sampling. Application of the model to the meso and racemic diads in PS confirms the fact that conformational mobility of the chain plays a major role in intramolecular exclmer formation. Comparison with experiments demonstrates that the decay of the monomer fluorescence in styrene dimers is predominantly governed by the process of conformational transitions. 

The platelet particles are incorporated in a lacquer of defined thickness on a standard black and white drawdown card. The card is mounted on a rotatable sample holder and measured under (A) 0°j45° (diffuse reflection) and (B) 22.5°/22.5° (regular reflection, luster)... 

Calculation of the Corrected Value of the 11 Al Chemical Shift in Various Zeolites from the Spectra of Stationary Samples at 16 MHz and of Rotating Samples at 70 MHz -1 ... 

Blondel s method involves abrading a rotating sample in a rotating porcelain mortar filled with porcelain pellets. A variation on this method is dry friction of a plane surface with steel balls rolling under pressure. 

Phase identification was performed by X-ray diffraction in Bragg-Brentano geometry with Cu-Ka radiation and a secondary monochromator. A rotating sample holder was used in order to minimize texture effects in the x-y plane and to offset the effects of the rather large grain size. Diffractograms were taken as a function of depth after stepwise removal of layers with an abrasive diamond disk. 

B) turret mounted discrete filters, single detector and rotating sample cup (Dickey-John, Anburn, IL). 

A simple example of the use of LD/FTMS for surface analysis may be found in the analysis of blue stain on the surface of a copper part. In order to determine the nature of the stain, we obtained LD/FTMS spectra for samples of both stained and unstained copper. Both samples were mounted on the automatically rotated sample insertion probe on the FTMS-2000. The samples were rotated after each laser shot to expose a fresh surface at the laser focus. Approximately twenty-five laser shots were signal averaged for each spectrum, in order to increase signal-to-noise, and to provide a spectrum which would represent the averaged composition of the surface. 

Dyer, F. F., L. C. Bate, and J. E. Strain Three-Dimensionally Rotating Sample Holder for 14-Million Electron Volt Neutron Irradiations. Anal. Chem. 39, 1907 (1967). 

In some cases it is desirable to rotate the sample and keep it cool at the same time. A cell that allows the measurement of Raman spectra of rotating samples at liquid-nitrogen temperatures has been designed (42). A rotating... 

Here, T is the observed line width (Av << F), 7d is the peak-to-valley intensity in the difference spectrum, and To is the peak height of the Raman line. Although this equation is for Lorentzian-shaped bands, the results are approximately the same for Gaussian-shaped bands (the constant 0.385 becomes 0.350). In the case of carbon disulfide-benzene mixtures, the smallest shift observed was -0.06 cm-1, and the associated error was 0.02 cm-1 (77). A convenient rotating system that can be used for (1) difference spectroscopy, (2) normal rotating sample techniques (solid and solution), and (3) automatic scanning of the depolarization ratios as a function of the wave number has been designed (45). 

Figure 3 illustrates the concepts of Raman cells that can be used for experiments under reaction conditions. Several commercial cells are suitable for use in combination with Raman microscopy. The rotating sample design was modified by Wachs s group (Figure 3A, Banares et al., 1994) and used to investigate supported oxides during selective alkane oxidation (Banares et al., 2000C Guliants et al., 1995 Sim et al., 1997) and various catalysts...

FIGURE 4.34 Variation in the AE signal of three different samples while polishing with no wafer rotation. Samples were polished with ISOrpm at 3psi (from Ref. 36). 

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