Fourier transform near-infrared Raman determination

Fourier transform near-infrared spectroscopy had been used to determine traces of hydroxy and carboxy functional groups and water in polyesters. Bowden and co-workers [25] monitored the degradation of PVC using Raman microline focus spectrometry. They demonstrated that PVC decomposition is accompanied by the formation of modal polyene chains containing 11-12 or 13-19 double bonds. Bloor [26] has discussed the Fourier transform Raman spectroscopy of polydiacetylenes. Koenig [27] discusses results obtained by the application of infrared and Raman spectroscopy to polymers. 

I J Williams, RE Aries, DJ Cutler, DP Lidiard. Determination of gas oil cetane number and Cetane Index using near-infrared Fourier transform Raman spectroscopy. Anal Chem 62 2553-2556, 1990. MB Seasholtz, DD Archibald, A Lorber, BR Kowalski. Quantitative analysis of liquid fuel mixtures with the use of Fourier transform near-IR Raman spectroscopy. Appl Spectrosc 43 1067-1072, 1989. 

Commercial analyzers mainly intended for laboratory use have been adapted with optical fibers to most spectrophotometers (Photonetics Sodety). Assemblies of fibers on spec-trofluorimeters [82,199] and Raman [167,177,193,200], infrared (IR), near-IR [189] mid-IR [201], and Fourier transform (FT) IR [202,203] spectrometers have already proved their value for remote spectroscopic sensing. However, these units are only partially adequate for continuous in situ process control because of their weak dynamic range after coupling of fibers and a maladjusted numerical aperture with respect to optical fibers. Photodiode-array instruments, without spectral scanning, are nevertheless the best for on-line control. This class includes the series of Hewlett-Packard HP 8450-8452 spectrophotometers and the Fluo 2(X)1 spectrometer (Dilor Society) [175] for fluorimetric and Raman determinations. 

Pioneering work by the Alix laboratory on the secondary structure of human elastin and the solubilized K-elastin, estimated the molecule to be composed of 10% a-helices, 35% P-strands and 55% undefined conformation. These estimations were based on Fourier transform infrared (FTIR), near infrared Fourier transform Raman spectroscopy and circular dichroism (CD) (15). To further investigate the nature of the elasticity, polypeptides of hydrophobic sequences containing exons 3, 7, and 30 of human elastin were analyzed by CD and Classic Raman spectroscopy, revealing polyproline II (PPII) helix secondary structures in both the aqueous and solid phase. Further analysis of exon 30 by FTIR spectroscopy determined that this sequence was characterized by both PPII as well as p-sheets structures (15). The presence of these structures were dependent on temperature, concentration and / or time, where lower temperatures and concentrations favored the PPII structure and higher temperatures and concentrations favored p-sheets (16). 

Because the IV is a measure of the relative unsaturation of a compound or sample, other analytical techniques (e.g., gas chromatography of FA composition, AOCS Cd lc-85) can be used to estimate the value. Interest in recent years has focused on spectroscopic techniques for the rapid determination of TV. Fourier transform (FT)-near-infrared, near-infrared, FT-Raman, and H and nuclear magnetic resonance (NMR) spectroscopic techniques have all been investigated (Ng and Gee, 2001). The most promising results have been obtained with FT-near-infrared spectroscopy, which only takes a few minutes to determine the iodine value (Cox et al., 2000). 

Infrared and nuclear magnetic resonance spectroscopy are the most important spectroscopic methods for analyzing coating materials. Near infrared Fourier transform (NIRFT) Raman spectroscopy [10.8] also has great potential, particularly for aqueous systems. UV/VIS spectroscopy is used only in exceptional cases, e.g., to determine light protection agents (UV absorbers). 

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