Samples and Data Acquisition

Data taken from R. Jenkins and R.L. Snyder, Introduction to X-ray Powder Diffractometry, John Wiley Sons Inc., New York. 1996 John Wiley Sons Inc. 

Another sample-related issue is that X-ray penetration into matter is limited because of X-ray absorption in matter. A certain depth from the surface can only be examined. Table 2.3 lists typical penetration depths for three types of materials. Obviously, X-rays penetrate deeper in materials composed of lighter elements than those of heavy elements. 

Spectrum matching is determined by the positions of the diffraction peak maxima and the relative peak intensities among diffraction peaks. 

In a modern diffractometer, data acquisition and treatment are mainly done by computer. To obtain adequate and data of sufficient quality for identifying a material, the following factors are important  

To obtain a satisfactory diffraction spectrum, the following treatments of diffraction data treatment should be done  

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As liquid chromatography plays a dominant role in chemical separations, advancements in the field of LC-NMR and the availability of commercial LC-NMR instrumentation in several formats has contributed to the widespread acceptance of hyphenated NMR techniques. The different methods for sampling and data acquisition, as well as selected applications will be discussed in this section. LC-NMR has found a wide range of applications including structure elucidation of natural products, studies of drug metabolism, transformation of environmental contaminants, structure determination of pharmaceutical impurities, and analysis of biofiuids such as urine and blood plasma. Readers interested in an in-depth treatment of this topic are referred to the recent book on this subject [25]. 

Stress MS has been applied to the study of polymers for 15 years, and several diflFerent devices have been developed for these studies. In the following sections, we discuss mass spectrometers for stress MS, devices for mechanically loading polymeric samples, and data acquisition and analysis techniques. 

At present, there is no lack of commercially available FIA instruments that can be interfaced with sampling and data acquisition devices or used in combination with other flow methodologies or more recent flow devices. Many of these instruments (fluorimeters, atomic absorption spectrometers, etc.) offer compact setup suited to specific purposes. 

The above approach for correcting shifts in the laser wavelength can be employed in the laboratory but is more applicable to the process environment where the sample and data acquisition parameters are similar sample after sample. The drawback in the analytical or research laboratory is that a number of different samples can be encountered which possess a variety of different Raman-scattering cross sections. In order to prevent detector saturation, it may be necessary to adjust the percentage of sampled laser emission for each Raman sample (and its associated exposure parameters). This can be inconvenient therefore, in the laboratory, an alternative method of laser wavelength calibration is proposed. 

For a detailed discussion of the art of sample handling and data acquisition for blood gas measurements, see National Committee for Clinical Laboratory Standards. Blood gas pre-analytical considerations specimen collection, calibration, and controls Proposed Guideline. NCCLS publication C27-P, Villanova, Pennsylvania, NCCLS, 1985... 

Once the microcomputer has received this information, a ready light is turned on and data acquisition can be begun by pushing a start button, A busy light then flashes to indicate that data collection is in progress. After the sample breaks, the operator... 

All modern heat flow calorimeters have twin cells thus, they operate in the differential mode. As mentioned earlier, this means that the thermopiles from the sample and the reference cell are connected in opposition, so that the measured output is the difference between the respective thermoelectric forces. Because the differential voltage is the only quantity to be measured, the auxiliary electronics of a heat flux instrument are fairly simple, as shown in the block diagram of figure 9.3. The main device is a nanovoltmeter interfaced to a computer for instrument control and data acquisition and handling. The remaining electronics of a microcalorimeter (not shown in figure 9.3) are related to the very accurate temperature control of the thermostat and, in some cases, with the... 

The thickness of pharmaceutical tablet coatings was predicted using target factor analysis (TFA) applied to Raman spectra collected with a 532-mn laser, where the samples were photobleached in a controlled manner before spectra were acquired. The authors acknowledge numerous issues that limit the direct applicability of this approach to process control. These include potential damage or alteration of the samples from photobleaching, laser wavelength selection, and data acquisition time. However, most of the issues raised relate to the hardware selected for a particular implementation and do not diminish the demonstration [286]. 

Both new and experienced users can take advantage of software to lead them through instrument set-up and data acquisition. Automated quantitation routines are available to calculate compound amounts in samples. These routines offer complete flexihihty to generate custom report formats. By integrating retention time information and internal or external cahhration curves can he calculated. Quantitation data can he exported to popular spreadsheet programs. 

A microcomputer based control and data acquisition system is required to monitor the 10 thermocouples in the sample and to control the heater temperature. For the latter, the rate of change of the thermocouple in the slab was used and power to the cartridge heaters varied. Details are given by Duever (3) and in a WCPD report (4). 

Focused X-ray beam (at Beam Line 15A) was used for this study. In order to improve the resolution, the focused beam (about 1 x 1.5 mm) was cut into 0.9-0.5 mm O by apertures which were set just in front of the cell. Modulation frequency was 10 Hz. Scanning X-Y stage which was originally developed for the laser microscopy was set perpendicular to the surface of the iron-base table and scanning and data acquisition were controlled by PC-9801 VM2 microcomputer (NEC Co. Ltd.) with the original program Various size and shape of metal foils were glued on the paper to have a model patterned sample. 

Gel Permeation Chromatography. A Water Associates model 200 gel permeation chromatograph fitted with five Styragel columns having nominal porosity designations 107, 107,106, 1.5 X 105, and 1.5 X 104 A was used for the analysis of molecular weight distribution in TFE at a temperature of 50.0 0.5°C and a flow rate of 1.00 =t 0.05 ml/min. Further details concerning instrumental and operational parameters, sample preparation and injection, and data acquisition and reduction have been reported elsewhere (I). 

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