Four reflectance spectroscopy

To illustrate some commonly encountered classification methods, a data set obtained from a series of polyurethane rigid foams will be used [76]. In this example, a series of 26 polyurethane foam samples were analyzed by NIR diffuse reflectance spectroscopy. The spectra of these foams are shown in Figure 12.16. Each of these foam samples belongs to one of four known classes, where each class is distinguished by... 

The interaction of cupric ions with alumina supports has subsequently been studied more extensively as a function of the support surface area, metal loading, and calcination temperature (93,279) by means of EXAFS and X-ray absorption-edge shifts, in conjunction with XRD, EPR, XPS, and optical reflectance spectroscopy. These techniques, each sensitive to certain structural and electronic aspects, allow a unified picture of the phases present and the cation site location. Four Cu2 + ion sites are distinguished in the catalysts. In low concentrations (typically below about 4 wt. % Cu/100 m2/g support surface area) Cu2 + ions enter the defect spinel lattice of the A1203 support. The well-dispersed surface copper aluminate has Cu2+ ions predominantly occupying tetragonally (Jahn-Teller) distorted octahedral sites, although... 

The action of all UV absorbers depends on the Lambert-Beer law, and the absorption properties of the UV absorber. The further the absorption edge extends into the near UV region, the more UV light can be filtered out. Of the four UV absorber classes shown above, the hydroxyphenylbenzotriazoles have the broadest absorption band [5.8], [5.12], In addition to thermal stability [5.12] and stability to extraction with water or organic solvents, photochemical stability is important [5.13]-[5.15], Ultraviolet reflection spectroscopy can be used to establish whether the employed UV absorber is still effective, even after several years external weathering [5.16]. 

Reflectance spectroscopy concerns the measurement of four distinct types of materials and their interaction with light. Specular materials reflect the predominant amount of radiation at an angle equal and opposite to the incident radiation. Diffusely reflective materials scatter light over a wide range of angles, with the perfectly diffuse (or Lambertian) scatterer exhibiting a cosine response to the incident radiation. Gonioapparent... 

Exciton and inter band transitions for four PDAs as observed by reflection and electro-reflection spectroscopy [Sebastian and Weiser [75)3. 

FT-IR attenuated total reflectance spectroscopy was conducted using a PerkinElmer Spectrum One instrument equipped with a single bounce, diamond ATR accessory. Each spectrum was produced by 32 scans at a resolution of 4 cm. Four spectra were collected around the circumference of the cured rods with approximate 90° inerements. Then the collected 4 spectra of each resin were averaged for further analysis. 

Table 1 lists some of the properties of the plant-type iron sulfur-proteins for which extensive study by EPR and Mossbauer spectroscopy has been reported. The physical properties summarized show that the plant-type iron sulfur proteins have molecular weights in the range from 12,000 to 24,000 and have EPR g-values (gx, gy, gz) all of the g = 1.94" type shown in Fig. 6 but with minor variations reflecting axial or nonaxial symmetry of the paramagnetic center. The amino-acid sequences of four plant-type iron-sulfur-proteins are known alfalfa (136), L. glauca (137), Scenedesmus (138), and spinach (139). Each protein has about 97 residues, all in a single peptide chain these are shown in Table 2. 

Identifying pharmaceuticals, whether APIs or excipients used to manufacture products, and the end products themselves is among the routine tests needed to control pharmaceutical manufacturing processes. Pharmacopoeias have compiled a wide range of analytical methods for the identification of pharmaceutical APIs and usually several tests for a product are recommended. The process can be labor-intensive and time-consuming with these conventional methods. This has raised the need for alternative, faster methods also ensuring reliable identification. Of the four spectroscopic techniques reviewed in this book, IR and Raman spectroscopy are suitable for the unequivocal identification of pharmaceuticals as their spectra are compound-specific no two compounds other than pairs of enantiomers or oligomers possess the same IR spectrum. However, IR spectrometry is confronted with some practical constraints such as the need to pretreat the sample. The introduction of substantial instrumental improvements and the spread of attenuated total reflectance (ATR) and IR microscopy techniques have considerably expanded the scope of IR spectroscopy in the pharmaceutical field. Raman spectroscopy,... 

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