Fourier transform near-infrared Raman spectroscopy

6 Fourier Transform Near-Infrared Raman Spectroscopy 

The appearance of the Raman spectra is essentially independent of the physical form of the sample. The only obvious difference between spectra of pellets, powders, films, fibres, and foams is in the signal intensity. For constant laser power these intensities 

The quality of the spectra obtained in two minutes is more than adequate for qualitative identification. Differences in crystallinity are readily seen for both PP and polyester samples. Some common inorganic fillers such as glass and talc are weak Raman scatterers and are not evident in the spectra. In other cases inorganic fillers are seen, e.g., BaS04 in voided polyethylene terephthalate film. 

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The advantages of Fourier transform near-infrared Raman spectroscopy are ... 

Aghenyega and co-workers [24] have investigated the application of Fourier transform near-infrared Raman spectroscopy in the synthetic polymer field. Their investigations covered the following areas ... 

B. Chase, Fourier transform near-infrared Raman spectroscopy, in Handbook of Vibrational Spectroscopy, J. C. Chalmers and P. R. Griffiths, Eds., Wiley, Chichester, West Sussex, England, 2002, Vol. 1, p. 522. 

Under non-resonant conditions, quantum yields for the Raman effect are in the order of 10 , implying that sample concentrations in the millimolar range are required for obtaining Raman spectra of satisfactory quality. Resonance enhancement substantially improves the sensitivity, but even RR intensities are too weak to obtain spectra of samples which exhibit a strong fluorescence or which contain strongly fluorescent impurities. In those cases, Fourier-transform near-infrared Raman spectroscopy may be a useful alternative approach. 

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. 

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. 

Choquette, S. J., et al. "Identification and Quantitation of Oxygenates in Gasoline Ampules Using Fourier Transform Near-Infrared and Fourier Transform Raman Spectroscopy." Analytical Chemistry, 681996,3525-3533. 

SJ Choquette, SN Chester, DL Duewer, S Wang, TC O Haver. Identification and quantitation of oxygentates in gasoline ampules using Fourier transform near-infrared and Fourier transform Raman spectroscopy. Anal Chem 68 3525-3533, 1996. 

Near-infrared surface-enhanced Raman spectroscopy Some of the major irritants in Raman measurements are sample fluorescence and photochemistry. However, with the help of Fourier transform (FT) Raman instruments, near-infrared (near-IR) Raman spectroscopy has become an excellent technique for eliminating sample fluorescence and photochemistry in Raman measurements. As demonstrated recently, the range of near-IR Raman techniques can be extended to include near-IR SERS. Near-IR SERS reduces the magnitude of the fluorescence problem because near-IR excitation eliminates most sources of luminescence. Potential applications of near-IR SERS are in environmental monitoring and ultrasensitive detection of highly luminescent molecules [11]. 

Fourier transform mid-infrared (FTIR), near-infrared (FTNIR), and Raman (FT-Raman) spectroscopy were used for discrimination among 10 different edible oils and fats, and for comparing the performance of these spectroscopic methods in edible oil/fat studies. The FTIR apparatus was equipped with a deuterated triglycine sulfate (DTGS) detector, while the same spectrometer was also used for FT-NIR and FT-Raman measurements with additional accessories and detectors. The spectral features of edible oils and fats were studied and the unsaturation bond (C=C) in IR and Raman spectra was identified and used for the discriminant analysis. Linear discriminant analysis (LDA) and canonical variate analysis (CVA) were used for the disaimination and classification of different edible oils and fats based on spectral data. FTIR spectroscopy measurements in conjunction with CVA yielded about 98% classification accuracy of oils and fats followed by FT-Raman (94%) and FTNIR (93%) methods however, the number of factors was much higher for the FT-Raman and FT-NIR methods. 

IR spectroscopy became widely used after the development of commercial spectrometers in the 1940s. Double-beam monochromator instruments were developed, better detectors were designed, and better dispersion elements, including gratings, were incorporated. These conventional spectrometer systems have been replaced by Fourier transform IR (FTIR) instrumentation. This chapter will focus on FTIR instrumentation and applications of IR spectroscopy. In addition, the related techniques of near-infrared (NIR) spectroscopy and Raman spectroscopy will be covered, as well as the use of IR and Raman microscopy. 

A. Matsushita, Y. Ren, K. Matsukawa, H. Inoue, Y. Minami, I. Noda, Y. Ozaki. Two-dimensional Fourier-transform Raman and near-infrared correlation spectroscopy studies of poly (methyl methacrylate) blends. 1. Immiscible blends of poly (methyl methacrylate) and atactic polystyrene. Vib Spectmsc 24 171, 2000. 

C.M. Deeley, R.A. Spragg and T.L.A. Threlfall, Comparison of Fourier transform infrared and near-infrared Fourier transform Raman spectroscopy for quantitative measurements an application, Spectrochim. Acta, Part A, 47A, 1217-1223 (1991). 

However, the high frequency of the laser irradiation in the visible region may lead to photochemical reactions in the laser focus. Besides, fluorescence can often cover the whole Raman spectrum. Such problems can be avoided by using an excitation wavelength in the near-infrared (NIR) region, e.g. with an Nd YAG laser operating at 1064 nm. Deficits arising from the v dependence of the Raman intensity and the lower sensitivity of NIR detectors are compensated by the Fourier-Transform (IT) technique, which is widespread in IR spectroscopy . ... 

Fourier-Transform Infrared (FTIR) spectroscopy as well as Raman spectroscopy are well established as methods for structural analysis of compounds in solution or when adsorbed to surfaces or in any other state. Analysis of the spectra provides information of qualitative as well as of quantitative nature. Very recent developments, FTIR imaging spectroscopy as well as Raman mapping spectroscopy, provide important information leading to the development of novel materials. If applied under optical near-field conditions, these new technologies combine lateral resolution down to the size of nanoparticles with the high chemical selectivity of a FTIR or Raman spectrum. These techniques now help us obtain information on molecular order and molecular orientation and conformation [1],... 

There is a real chance of a breakthrough of Raman spectroscopy in routine analytics. Excitation of Raman spectra by near-infrared radiation and recording with interferometers, followed by the Fourier transformation of the interferogram into a spectrum -the so-called NIR-FT-Raman technique - has made it possible to obtain Raman spectra of most samples uninhibited by fluorescence. In addition, the introduction of dispersive spectrometers with multi-channel detectors and the development of several varieties of Raman spectroscopy has made it possible to combine infrared and Raman spectroscopy whenever this appears to be advantageous. 

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