Difference absorption spectrophotometry spectra

Test B Examine by IR absorption spectrophotometry, according to the general method (2.2.24), comparing with the spectrum obtained with omeprazole CRS. If the spectra obtained in the solid state show differences, dissolve the substance to be examined and the reference substance separately in methanol R, evaporate to dryness and record new spectra using the residues. 

Although its precise structure has not yet been settled, the hydrated electron may be visualized as an excess electron surrounded by a small number of oriented water molecules and behaving in some ways like a singly charged anion of about the same size as the iodide ion. Its intense absorption band in the visible region of the spectrum makes it a simple matter to measure its reaction rate constants using pulse radiolysis combined with kinetic spectrophotometry. Rate constants for several hundred different reactions have been obtained in this way, making kinetically one of the most studied chemical entities. 

The lack of a well defined UV absorption spectrum for phenytoin makes its determinations by direct UV spectrophotometry difficult nevertheless, the literature describes several methods which depend upon the spectrum of the unchanged drug25 Wallace et al 6 and Fellenberg et al reviewed the use of UV spectrophotometric methods for the analysis of phenytoin. A spectrophotometric method for the quantitative determination of phenytoin has been described by Bgorge et al B based on the difference in absorbance of an alcoholic solution at 233 nm before and after conversion of phenytoin to the sodium salt. Methods that require conversion of the drug to benzophenone have been reported Sf30,31,32 ... 

Some solids interact with solvents. In this case, the absorption spectrum of the solution will be different from that of the solid. For these solids and for insoluble solids, reflectance spectrophotometry would be a suitable technique for characterising the solids. More expensive spectrophotometers are provided with an integrating sphere, which allows for diffuse reflectance measurements. Less satisfactory results are obtained by preparing a nujol mull of a small amount of the solid. Impregnate a rectangular strip of filter paper with the mull and press it against the wall of a spectrophotometer cell. 

Shiba et al., 1993 [308] made a near-infrared spectrophotometry for 52 T Tauri stars in the Taurus-Auriga region in the wavelength range from 0.9 to 2.5 micrometers. In more than half of their used sample, wide and shallow dips due to water vapor are superposed at 1.4 and 1.9 micrometers on the spectra. For the central star a spectrum was assumed and after decomposition of the spectra into central star and disk components, the water vapor bands still remain in the disk component therefore the conclusion is that water vapor is located in the disk component of at least 17 T Tauri stars (33%) of the sample. The temperature of the water vapor is about 2000 K which can be estimated from the width of the absorption bands. Certainly such water molecules could exist at different temperatures over the entire disk. In the outer... 

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