Vibrational spectroscopy degradation

VIBRATIONAL SPECTROSCOPY OF CHEMICAL AGENTS SIMULANTS, DEGRADATION PRODUCTS OF CHEMICAL AGENTS AND TOXIC INDUSTRIAL COMPOUNDS... 

In this paper several Chemical Warfare Agents Simulants (CWAS), some of their hydrolysis and degradation products, and Toxic Indnstrial Compounds (TIC s) were analyzed nsing vibrational spectroscopy. The objective of this work is to characterize the spectroscopic signatures of these threat compounds and to demonstrate, at laboratory scale, the capability of Infrared and Raman spectroscopy for generating methodologies for detection of CWA and TIC s. 

FE Barton 11, DS Himmelsbach, DE Akin, A Sethuraman, and K-E Eriksson. Two-Dimensional Vibrational Spectroscopy. Ill Interpretation of the Degradation of Plant Cell Walls by White Rot Fungi. Near Infrared Spectrosc. 3 25-34,1995. 

Oxidation is accelerated if the temperature is elevated. Exposure to optical and UV radiation can also accelerate the degradation. Additionally, the thermooxidation and photooxidation are accelerated by generating chemical effects by the application of mechanical forces (i.e., mechano-chemical degradation). Vibrational spectroscopy is particularly usefiil for studying the degradation processes as the measurements can be made in real time. 

G. Ellis, J. del Pino, C. Marco, M. A. Gomez, and J. G. Fatou, Structural effects on the thermal degradation of main-chain thermotropic Uquid crystal polyesters. Vibrational Spectroscopy, 9, 43 (1995). 

F. E. Barton, II, D. S. Himmelsbach, D. E. Akin, A. Sethuraman, K. -E. L. Eriksson. Two-dimensional vibrational spectroscopy HI interpretation of the degradation of plant cell walls by white rot fungi. J Near Infrared Spectrosc 25-34, 1995. 

Many analytical techniques used to inspect the cited properties are common to the field of polymer characterization vibrational spectroscopy (ETIR, Raman), magnetic resonance spectroscopy (NMR, ESR) and liquid chromatography (GPC, HPLC). A few methods, such as oxygen consumption and chemiluminescence, are more specific to oxidative degradation. Mechanical tests are frequently used in combination with other analytical tools to asset the effects of degradation on mechanical properties. 

Medel FJ, Rimnac CM, Kurtz SM. On the assessment of oxidative and microstructural changes after in vivo degradation of historical UHMWPE knee components by means of vibrational spectroscopies and nanoindentation. J Biomed Mater Res 2008. Published online. 

Another valuable advantage of Raman spectroscopy, which is unique, is its capability of being used to characterise carbon species, in particular graphitic and amorphous carbon this can be of value to many degradation and pyrolysis studies. Perfectly ordered graphite is characterised by a Raman-active vibrational mode that occurs at 1,575 cm-1 this band is usually referred to as the C7 band. With increasing disorder in the carbon, a new band, the D band, appears at... 

The initial observation is that PMMA is essentially completely degraded to monomer by heating to 375°C in a sealed tube while heating a mixture of red phosphorus and PMMA under identical conditions yields a solid, non-deqraded, product as well as a lower yield of monomer. One may observe, by 3C NMR spectroscopy, that the methoxy resonance is greatly decreased in intensity and methyl, methoxy phosphonium ions are observed by 31P NMR. Additional carbonyl resonances are also seen in the carbon spectrum, this correlates with a new carbonyl vibration near 1800 cm 1 in the infrared spectrum and may be assigned to the formation of anhydride. The formation of anhydride was also confirmed by assignment of mass spectra obtained by laser desorption Fourier transform mass spectroscopy, LD-FT-MS. 

Contemporary approaches to chemical stmcture elucidation are now heavily reliant on mass spectrometry and NMR spectroscopy. Since the advent of 2D NMR methods, in many laboratories vibrational data are either not acquired or not considered, which represents a paradigm shift from approaches to chemical structure elucidation as recently as 20 years ago when vibrational spectroscopic data were an integral part of the structure elucidation data assembled to characterize an unknown structure. In contrast, we have found it useful to continue to acquire and utilize vibrational data for the characterization of impurities and degradation products [64,65]. 

The major peculiarities for a diagenetically altered bone are an increase in crystal size and a decrease in protein content [104], thus complementary information on the state of degradation can be obtained by FT-IR (Fourier transform infrared spectroscopy). The characteristic splitting of the double peak at 563-604 cm-1 corresponds to the phosphate vibrations v4 (P04)3- indicating mineral-phase modifications, e.g. changes in crystallinity. A low value for the splitting factor SF indicates a high amount of amorphous material in the mineral phase and was obtained as described in Ref. [105],... 

The tables that follow contain information on the Chemical Warfare Agents Simulants (Table 2), degradation products of actual chemical agents (Table 3) and on the Toxic Industrial Compounds (Table 4) studied. Raman Spectroscopy and Fourier Transform Infrared Spectroscopy were used for the vibrational analysis. Spectra were compared to... 

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