Sample preparation, near

Near-infrared spectroscopy is quickly becoming a preferred technique for the quantitative identification of an active component within a formulated tablet. In addition, the same spectroscopic measurement can be used to determine water content since the combination band of water displays a fairly large absorption band in the near-IR. In one such study [41] the concentration of ceftazidime pentahydrate and water content in physical mixtures has been determined. Due to the ease of sample preparation, near-IR spectra were collected on 20 samples, and subsequent calibration curves were constructed for active ingredient and water content. An interesting aspect of this study was the determination that the calibration samples must be representative of the production process. When calibration curves were constructed from laboratory samples only, significant prediction errors were noted. When, however, calibration curves were constructed from laboratory and production samples, realistic prediction values were determined ( 5%). 

Gel phase fraction was measured on samples (see Ref. 14 for more details) formed beyond the gel point. One can see in Fig. 8 that G is a linear function of the stoichiometric ratio. Concerning this figure two comments have to be made. The p value corresponding to the stoichiometric ratio at which the gel phase is nul (p = 0.5639) is very different from the ifferent batches of monomers were used for the preparation of the two series of samples. A small but finite gel phase was measured below p (G = 1.6 10 at p = 0.5632) this could be due to either experimental imprecision on G or the fact that this sample prepared near the gel point contains very large polymer clusters of finite size which could not pass through the membrane used for the sol extraction. This result, G P is a linear function of p with a P-exponent value deduced from x and y exponent values measured below the gel point, indicates that below and beyond the gelation threshold, the percolation theory is well adapted to describe the properties linked to connectivity of polymer clusters formed by polycondensation. 

Mark, H. "Use of Mahalanobis Distances to Evaluate Sample Preparation Methods for Near-Infrared Reflectance Analysis", Anal. Chem. 1987 (59) 790-795. 

Results The raw data consisted of peak height ratios of signal internal standard, see data files VALIDl.dat (primary validation m - 0 repeats at every concentration), VALID2.dat (between-day variability), and VALID3. dat (combination of a single-day calibration with several repeats at 35 and 350 [ng/mlj in preparation of placing QC-sample concentration near these values). Fig. 4.29 shows the results of the back-calculation for all three files, for both the lin/lin and the log/log evaluations. Fig. 4.30 shows the pooled data from file VALID2.dat. 

Figure 1 shows narrow range high resolution scans of the molecular ion region of NDMA, recorded near the maximum of the GC peaks, present in one of the beer samples prepared in the AOAC collaborative study. The peak at m/z 74.0480 represents approximately 0.15 ng of NDMA injected on the column, corresponding to a concentration of 0.6 yg/kg of beer. Use of high resolution MS permitted confirmation of the identity and amount of nitrosamine without additional cleanup of the concentrate prepared by the AOAC method. Sample quantity requirements were comparable to those of the TEA. 

According to the characterizations by TEM and XRD, the sample prepared from a CH4/H2 plasma was composed of nanocrystalline diamond and disordered microcrystalline graphite. Then nondiamond carbon was effectively removed with an increase in [CO]. It is therefore concluded that the VDOS of the nanocrystalline diamond and DEC films extracted from the HREELS data is in qualitative agreement with the characterizations of TEM and XRD. Although the HREELS probes only the region near the surface, the agreement suggests that the surface dynamics do not differ dramatically from those of the bulk. 

Controlled sample preparation is difficult near the gel point where the rate of property change is largest. Physical gelation usually proceeds too rapidly so that the material near the gel point eludes the experiment or the application. However, chemical gelation is most suitable for controlling the evolving network structure. Several approaches have been explored in industrial applications and in research laboratories ... 

Direct insertion probe pyrolysis mass spectrometry (DPMS) utilises a device for introducing a single sample of a solid or liquid, usually contained in a quartz or other non-reactive sample holder, into a mass spectrometer ion source. A direct insertion probe consists of a shaft having a sample holder at one end [70] the probe is inserted through a vacuum lock to place the sample holder near to the ion source of the mass spectrometer. The sample is vaporized by heat from the ion source or by heat from a separate heater that surrounds the sample holder. Sample molecules are evaporated into the ion source where they are then ionized as gas-phase molecules. In a recent study, Uyar et al. [74] used such a device for studying the thermal stability of coalesced polymers of polycarbonate, PMMA and polylvinyl acetate) (PVAc) [75] and their binary and ternary blends [74] obtained from their preparation as inclusion compounds in cyclodextrins. 

NIR (near-infrared) imaging has also been well introduced into polymer characterization, mainly because no laborious sample preparation is necessary. Spatial resolution approaches the range of mid-infrared imaging. 

The OLED is composed of hard and soft layers so that the conventional cross-sectional TEM sample preparation techniques cannot be applied. Figure 10.3 is a first DB microscopy-prepared TEM image of an OLED in cross-sectional view [37], The glass substrate, ITO, organic layers, and A1 cathode are indicated in the image. The microstructure and interfaces of all these layers can be well studied now. The nanometer-sized spots in organic layers are indium-rich particles. We believe the combination of DB microscopy and TEM will greatly advance the OLED research and development in the near future. 

In terms of sample preparation, we indicated that in nearly every case, preanalysis procedures must be performed to get the sample into a form that can be utilized by the chosen analytical method. Common sample preparation schemes can involve any number of physical or chemical processes, such as drying, dissolving, extracting, or chemical alteration. 

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