Spectrophotometer spectroscopy, applied

Spectroscopy is another method used to detect art forgeries. In spectroscopy, electromagnetic radiation is applied to the substance or substances under consideration. The resulting spectra are recorded to identify the chemical composition of the substance or substances. When a spectrophotometer is used, the radiation, usually visible and invisible ultraviolet waves, can be applied to a solution in a tube, and the absorption of radiation is noted. For this type of analysis, a spectrophotometer must be available. 

For bands with similar widths, it is not possible to take advantage of the discriminative power of the derivatives. One can then use the zero crossing method. To the maximum or minimum of each band, there is a correspondence with a zero derivative value the concentration value of the compounds do not matter. To the inflexion point of the usual spectrum, the second derivative is zero, etc. To these particular points, the value of the derivative is due to the only contribution of the second compound and, in this way, the interference of the first one may be removed. This methodology was used at the very beginning of derivative spectroscopy and was mainly applied to those compounds that had close spectra. One has to note, however, that this methodology requires the use of very reproducible wavelength-positioning spectrophotometers. 

The concept of differentiating spectral data was first introduced in the 1950s, but it received little attention primarily because of experimental difficulties in generating derivative spectra with early ultraviolet (UV)/ visible (Vis) spectrophotometers. Use of mathematical or optical methods to generate derivative spectra became feasible with the advent of microprocessors and microcomputers in the late 1970s. Nowadays, most instruments offer at least the first and second numerical derivatives as a standard feature. The combination of derivative spectroscopy and chemometrics for calibration and data evaluation has further increased the popularity of this technique. Derivative techniques are applied especially in UV spectroscopy for pharmaceutical, biomedical, and environmental measurement tasks and in food research. 

To monitor UV-stabilization and discoloration (yellowing) during EVA weathering, UV-Visible spectroscopy is applied. UV-Visible transmittance measurements were carried out with a spectrophotometer type Cany 500 from Varian with integrate sphere. All UV-Visible spectra were recorded at 600 nm/min at 1 nm. 

Figure 1 Schematic diagram of a modem Raman spectrophotometer. Reproduced with kind permission by the publishers of Ref. 4. [Applied Spectroscopy, 51, Pajcini, V., et al., UV Raman Spectroscopy Spectral and Spatial Selectivity with Sensitivity and Simplicity, pp. 81-86, copyright 1997, Society for Applied Spectroscopy.]... 

Fig. 1.37. Rotational Raman spectrum of nitrous oxide gas (NNO) run on the Cary Model 82 Raman spectrophotometer with argon ion 5145 A excitation. From Sloane, used with permission from The Society for Applied Spectroscopy.

UV-Vis Spectroscopy The last step in the analysis of the generated powder is in most cases done by UV-Vis absorption spectroscopy. This technique is applied to measure two properties. A basic double beam spectrophotometer (UV-3600 Shimadzu) is used for the quantification of the composition of the generated powder. This is of uttermost interest in particular for the generation of solid dispersions. Another property that is measured by UV-Vis spectroscopy is the dissolution behavior of the generated powder. For all the UV-Vis measurements, a representative sample of the generated powder had to be dissolved again [1]. 

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