Compact sample

In direct insertion techniques, reproducibility is the main obstacle in developing a reliable analytical technique. One of the many variables to take into account is sample shape. A compact sample with minimal surface area is ideal [64]. Direct mass-spectrometric characterisation in the direct insertion probe is not very quantitative, and, even under optimised conditions, mass discrimination in the analysis of polydisperse polymers and specific oligomer discrimination may occur. For nonvolatile additives that do not evaporate up to 350 °C, direct quantitative analysis by thermal desorption is not possible (e.g. Hostanox 03, MW 794). Good quantitation is also prevented by contamination of the ion source by pyrolysis products of the polymeric matrix. For polymer-based calibration standards, the homogeneity of the samples is of great importance. Hyphenated techniques such as LC-ESI-ToFMS and LC-MALDI-ToFMS have been developed for polymer analyses in which the reliable quantitative features of LC are combined with the identification power and structure analysis of MS. 

The NMR measurement on water retained in the compacted sample was performed by using a Bruker CXP-200 NMR Spectrometer. 

Sample holders for determination of the Curie point exist basically as two different types. A compact sample, e.g. a metal block can be investigated by attachment on a normal, rod-type TG-sample holder (Fig. 8 k). The sample must be provided with a hole for the TG-rod, the built-in thermocouple should not have any contact... 

Several charge-transfer complexes of HMTTeF with TeNQs, p-quinone and other accepting re-acceptors have been prepared and electrical resistivities measured with compaction samples. 

B = Volume of compacted sample in ml Note The following wet slurry method of coating has been found satisfactory. Add... 

Another kind of effective or average optical constants involves mixtures of different particles such as atmospheric aerosols or soils. Effective optical constants for compacted samples of these mixtures might be inferred from reflectance and transmittance measurements as if the samples were homogeneous. But scattering or extinction calculations based on these optical constants would not necessarily be correct. 

Figure 5 shows the results of the authors study on the ability of NIR to monitor the scale-up from the laboratory Carver Press to the Fitzpatrick roller compactor. Because the NIR signal is influenced by changes in the physical and mechanical properties, multivariate data analysis techniques were used to identify and separate these contributions in the overall NIR signal. A flat-faced rectangular die and punch set, 40 x 15 mm in size, was fitted on the laboratory Carver Press to prepare tablets similar in shape and size to the roller compacted samples. 

Figure 5 Relationship between the slope of the NIR spectrum and the tensile strength of the corresponding roller compacted sample at different moisture quantities. Triangles, 3.5% diamonds, 4.6% circles, 5.7% and squares, 7.2% LOD samples.

Table 14 Root Mean Squares Errors for the NIR-PLS Predicted Values of Different Sample Attributes for the MCC Surrogate Tablets and Roller Compacted Samples...

The PLS model generated on samples prepared according to the Latin squares experimental design was used to predict the key compact attributes from the real-time spectral data collected for roller compacted samples (Fig. 8). Good agreement was observed between the NIR-predicted values and the values measured off-line using the reference methods (Table 16). 

The TS of the compacted samples was determined by transverse compression with a custom-built tensile tester. Tensile failure was observed for all the rectangular compacts when compressed between flat-faced platens at a speed ranging between 0.006 and 0.016 mm/sec. Platen speed was adjusted between materials to maintain a time constant of 15 2 seconds to account for viscoelastic differences the constant is the time between the sample break point and when the measured force equals Fbreak/e in the force versus time profile, where the denominator is the mathematical e. Specially modified punch and die sets permitted the formation of square compacts with a centrally located hole (0.11 cm diameter) that acted as a stress concentrator during tensile testing. This capability permitted the determination of a compromised compact TS and thus facilitated an assessment of the defect sensitivity of each compacted material. At least two replicate determinations were performed for each mechanical testing procedure and mean values are reported. 

Throughout the literature describing the compacted sample methodology, the choice of the binder material has time and again been pointed to as the most important aspect in determining source performance. Papers by Tong and Harrison [39], Mei and Harrison [40,41], Smith and coworkers [42,43], and Wayne [44] have... 

Just as the previously cited work illustrated the role of matrix selection in the quality of the mass spectra, Mei and Harrison [40] studied the underlying equilibrium involved in the formation and removal of metal oxides from the spectra of compacted oxide samples. The analyte for these studies was La203, chosen because of the high affinity of lanthanum for atomic oxygen, a product of the dissociation of both residual air and water vapor in compacted samples. Because the La-O bond strength is very high (8.30 eV), this oxide represents a case in which the dissociation of the original analyte would be difficult as well. On the basis of previous studies [41], it was assumed that approximately 50% of the lanthanum species sputtered from the surface would be free La atoms, and the other half would exist as oxides of one form or another. 

One remark talks about nano-hydrides become in fashion now. But it is necessary to realize that nearly all the metal hydrides are nano-materials initially, definitely. In the course of hydrogenation, the compact samples of metals (or IMCs) disintegrate into small particles which have (according microscopic or surface-area measurements) micro- (and not nano-) size. However, this does not speak yet for anything. These particles are not monocrystals, but - micro-sized conglomerates of nano-sized clasters (domains). These clasters have sometimes the structure, which differs from that, indicated (defined) by X-ray or neutron... 

Compaction of DDT powder has little effect on the suspensibility when the test is made on the fresh powder without a heat treatment however, after accelerated-storage pretreatment at 70 °C. for 2 hours, there is a consistent decrease in suspensibility with increasing compaction. Furthermore, compacted samples held in long-term storage exhibit the same pattern of loss of suspensibility as the samples subjected to accelerated-storage treatment. This is good evidence of the validity of the... 

Since the weighing of such small sample quantities can influence the analytical error, it is desirable to avoid the need to weigh the sample. One channel is occupied by the reference absorption measurement, for example with pure iron or low-alloy steels an iron hollow-cathode lamp is used and the measurement takes place at 372 nm. In this case, only one further element can be determined. The carrying out of the method is simple (Fig. 6). Tests of this compact sample technique with standard materials, of which there are at present only a few containing certified trace elements, show satisfactory agreement (Fig. 7). As regards traces, the chips of standard materials are very homogeneous. 

When samples are less homogeneous, this method can be repeated frequently, since the technique is simple and the time requirement relatively small. The numerous single results permit statistical calculations, and in general lead to the correct mean value. The detection limits in the compact sample method have not yet been found exactly, because the appropriate samples are not available but could lie in the range 10 s 10 7 weight percent. 

A temperature sensitivity study was made to establish the workability of the paving materials with increasing sulfur contents in the binders. Marshall compaction samples were prepared in quadruplicate for all the mixtures shown in Table II, and the effect of compaction at 10 temperatures was determined. Figures 4 and 5 show the results of the temperature sensitivity study on the Marshall stability of both methods of mixing with each aggregate. Figures 6 and 7 give the void content of the same... 

Resistance to the Solvent Action of Fuels. Sulfur—asphalt concretes were less affected by the solvent action of fuels than was normal asphaltic concrete. The solvent action of three fuels—gasoline, JP-4 jet fuel, and No. 2 diesel fuel—was tested on samples of normal asphaltic concrete and on 15-, 25-, and 35-vol % sulfur-asphalt concretes. Two test methods developed by McBee (15) were used to determine loss in weight and loss of stability on drip and total immersion testing of Marshall compaction samples. 

B = Volume of compacted sample in ml Note The following wet slurry method of coating has been found satisfactory. Add molten stearic acid at approx 70°C to a hot water slurry of RDX at approx 70° and then, after thorough mixing, cool, filter and dry the coated product... 

A solid compact sample or a tablet produced from powder may be placed directly in the sample holder. The spectrum is often improved by irradiating a fine hole within the sample with the laser beam and by analyzing the Raman radiation emerging from the hole. The multiple reflection of exciting and Raman radiation inside the hole enhances the efficiency of the transformation of laser radiation into Raman scattered radiation. 

Generally, the assumption is made that scattering does not depend on the wavenumber so that the conversion of the measured reflectance spectrum R by means of the Kubelka-Munk function F R), results in an absorption-proportional representation. As for ATR and reflection-absorption spectroscopy, also the diffuse-reflectance spectmm does not consist of dispersion features but band-like structures. For changes in low absorption, the sensitivity of diffuse reflectance is greater than the one of transmittance, while strong absorption bands are less pronounced in the diffuse-reflection (see Fig. 6.4-18). Therefore, diffuse-reflection spectra resemble poorly resolved transmittance spectra. For diffuse reflectance spectra where R is in the order of 0.01 or below, the function -log R or just I / R is equally well suited for conversion (Olinger and Griffiths, 1988). Such level are found with compact samples such as polymer foams or varnishes with filler (Otto, 1987 Korte and Otto, 1988). 

For particulate samples, and even more for compact samples exhibiting a smooth surface, it is crucial to prevent specularly reflected radiation from being detected together with the diffusely reflected component. To avoid this, the solid angle into which the incident radiation is specularly reflected should be excluded. Advantageously, irradiation normal to the surface (Korte and Otto, 1988) or out-of-plane configurations are used (see Fig. 6.4-19). As an alternative, a razor blade is vertically positioned on the surface as a blocker for surface-reflected radiation (Messerschmidt, 1985). 

With diffuse-reflection optics a reference signal cannot be measured without a standard. With reference to diluted samples, the matrix particulate is best suited. In this way, contaminations of the matrix which are virtually inevitable due to the large specific surface, are compensated for. For undiluted, specially compact samples, gold covered erasive paper has proved to be an excellent ready-to-use standard (Otto, 1987). 

Because high-energy photons exhibit only little absorption, reliable results are obtained with compact samples. Activation by photons is favourable if the sample contains macrocomponents with elements of high neutron absorption cross sections, such as Li, B, Cd, In or rare-earth elements. Furthermore, photon activation is applied for determination of elements that cannot be determined by (n,y) reactions, such as Be, C, N, O, F. These elements can be determined in concentrations down to about 10 g/g. Other elements such as Si, Zr and Pb can also be determined by (y,n) reactions. Examples are listed in Table 17.5. 

An alternative technique, which reduces segregation, is a unit-dose compacting sample thief (Fig. 2). Bias is still likely with this method because of the invasive nature of any sample thief... 

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