Sample holders, comparison

Figure 3. Comparison of the rate of oxidation of Fe(II) when mixed with apoferritin coats (480 Fe/molecule) in 0.15 M Hepes Na, pH 7.0, using absorbance at 420 nm ( a—s— ), availability to react with -phenanthroline ( o—o—o ), change in the x-ray absorption near edge structure (XANES) ( — — ). All three types of measurements were made under the same experimental conditions, including the sample holder. (Data are taken from Ref.

Fig. 7. Comparison of experimental scattering Intensity in two different sample holders (---- 6 mm,. 1 mm diameter) at 172 bar.

A comparison (24) of the sample holders used in the DSC-1, DSC-lB, and DSC-2 instruments is shown in Figure 6.37. In the DSC-1 cell, the sample and reference holder consisted of a stainless-steel cup and support, a platinum-wire sensor, an etched Nichrome heater, and other thermal parts. All these components were mechanically crimped together in a very tight sandwich. This sample holder operated well over the temperature range —125 to 500°C. In the DSC-2 sample holder, the materials of construction used are a platinum-iridium alloy for the body and structured members of the holder, a platinum wire for both the heater and sensor, and x-alumina for electrical insulation. All parts of the holder are spot-welded together. 

Care must be taken to ensure the slide is properly prepared to accept the continuous phase. Water-wet solids suspended in an oil phase can interact differently when prepared on a hydrophilic glass surface compared with a hydrophobic sample holder. Careful observation and comparison of suspension morphology using both hydrophilic and oleophilic sample holders are sometimes required to confidently characterize a suspension. The transmitted light technique is limited by the opaque nature of most oil samples, and in cases where the sample cannot be made thin enough, an alternative technique using reflected light is available. 

The slightly improved repeatability of the He- and Hf2-values in comparison with that of the Hfl-value might be caused by the improved thermal contact between sample and sample holder after the fusion process. Nakamura [5] reports a reproducibility of 3°C for the Tm/Tc determination. The difference between the repeatability and the reproducibility values of the Tm/Tc determinations is thus considerably higher than those found for the Tg(onset)-value determination. 

Additional advantages are offered by extending the applicability of the MALDI methods to insoluble polymers [65] and saturated polyolefins [66]. One of the key factors that influence the success and the quality of MALDI mass spec-trometric analysis is the sample preparation. Thus, prerequisites for traditional sample preparation method require soluble analytes and matrices and the compatibility of the solvents for both matrix and analyte systems, subsequent solvent removal, and the homogeneity of the crystallized analyte/matrix mixture on the surface of the MALDI sample holder [67-71]. These factors can introduce severe mass discrimination effects. The advantages of solvent-free preparation in comparison to conventional solvent-based MALDI-MS were recently reported [65, 72]. The MALDI mass spectra obtained by the solvent-free sample preparation method were compared by Trimpin et al. [72] with mass spectra obtained by conventional solvent-based MALDI-MS and by laser desorption (LD)-MS under identical experimental conditions, stressing the capability of solvent-free MALDI-MS to characterize insoluble samples. 

The actual color samples are in the form of l"xlV coated metal chips, housed in hinged plastic holders. While this reference collection is intended for color comparisons only, it is hoped that future research will allow for the distribution of corresponding chemical analysis data. 

For the diffraction technique, —325-mesh shale powders were packed into the 7/8-in. diameter by 1/16-in. deep cavity of a 1-in. diameter aluminum holder and pressed smooth with a glass plate. A Norelco-Phillips diffractometer equipped with a Cu(Ka) source was used to analyze the samples. The diffractometer was driven at l°/min and the intensity response of the nonrotating sample recorded on a strip chart recorder. Peak assignments in both cases were made by visual comparisons with standards. 

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