Near IR/Raman spectroscopy

Ryder, A.G., O Connor, G.M. and Glynn, T.J. (1999) Identifications and quantitative measurements of narcotics in solid mixtures using near-IR Raman spectroscopy and multivariate analysis /. Forensic Sci. 44, 1013-1019. 

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]. 

Near-IR Raman spectroscopy was used by Mehadevan-Jansen et al. [159] to differentiate cervical precancers from healthy or normal tissue. The algorithms generated may potentially separate benign abnormalities such as inflammation and metaplasia from precancers. 

C. Deeley, J. Sellors and R. Spragg, A Comparison of FT Near IR Raman Spectroscopy, with FT-IR Photoacoustic and Reflection Measurements of Polymers, Perkin Elmer Infrared Spectroscopy Applications 14.3, Perkin Elmer Corporation, Norwalk, CT, USA, 1988. 

Fourier transform near-IR Raman spectroscopy (400-10,000 cm ) is useful for the examination of additives in polymer extracts [9]. 

XL Shi, SJ Pams, KD Pennell, MD Morris. Detection of chlorinated hydrocarbons in aqueous surfactant solutions by near-IR Raman spectroscopy. Appl Spectrosc 49 1146-1150, 1995. 

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. 

The Raman spectra of heroin, morphine and codeine (Fig. 7.10) are highly characteristic because of the change in the bands due to the aromatic ring. The FT-IR spectra of these compounds are quite similar. Near-infrared Raman spectroscopy can provide a rapid method for characterising drugs with minimal sample preparation and analysis time. 

The drawback is the measurement time, which depends on the number of pixels. Spectrometer manufacturers therefore developed line mapping, in which samples are scanned line by line, thereby reducing the acquisition time. These devices were developed for Raman, IR, or near-IR (NIR) spectroscopy (with diode array detectors). However, due to the moving stage, this kind of imaging principle is only suitable for at-line applications. 

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 in the last decade by FTIR instrumentation. This chapter will focus on FTIR instrumentation and applications of IR spectroscopy. In addition, the related techniques of near-IR (NIR) spectroscopy and Raman spectroscopy will be covered. 

All three techniques (i.e., FT-IR, near-IR Raman, and photoaconstic spectroscopies) provided spectra suitable for qualitative identification qnickly and with little sample preparation. Raman and external reflection spectra can be obtained directly from large objects but for photoacoustic measurements the samples mnst be small. 

Vibrational spectroscopies (mid-IR, near-IR, Raman) play an important role in polymer/additive analysis. Optical advances as well as spectacular advances in computing technology and data processing algorithms have greatly impacted vibrational spectroscopy over the past 25 years (cfr Table 1.5). Rapid digital data acquisition is required for FTIR, FT-Raman or CCD-Raman spectroscopy. The raw data obtained from these instruments must always be manipulated before a recognisable spectrum can be displayed. 

Raman spectroscopy is one of the optical molecular spectroscopic techniques capable of giving quantitative information about molecular orientation in polymers. A resonant Raman-active agent and/or highly anisotropic rigid rod polymeric substance incorporated into polymers can be easily detected at low concentration levels and used as an indicator of the molecular orientation of the processed polymer itself [425]. It is possible to apply resonance Raman spectroscopy to many more problems. The combined application of UV/VIS and near-IR Raman excitation may be advantageous. UV excitation selects for a small number of resonance-enhanced bands of an analyte and the measurements are made with high sensitivity and selectivity. In contrast, with non-resonance visible and near-IR excitation, numerous Raman bands occur with similar intensities for all components in the sample in proportion to their concentrations. Consequently, one obtains both average and specific information on sample composition [419]. 

NIRIM Near-IR Raman imaging PA(S) Photoacoustic (spectroscopy)... 

As an alternative to wet ehemical routes of analysis, this monograph deals mainly with the direct deformulation of solid polymer/additive compounds. In Chapter 1 in-polymer spectroscopic analysis of additives by means of UV/VIS, FTIR, near-IR, Raman, fluorescence spectroseopy, high-resolution solid-state NMR, ESR, Mossbauer and dielectrie resonance spectroscopy is considered with a wide coverage of experimental data. Chapter 2 deals mainly with thermal extraction (as opposed to solvent extraction) of additives and volatiles from polymerie material by means of (hyphenated) thermal analysis, pyrolysis and thermal desorption techniques. Use and applieations of various laser-based techniques (ablation, spectroscopy, desorption/ionisation and pyrolysis) to polymer/additive analysis are described in Chapter 3 and are critically evaluated. Chapter 4 gives particular emphasis to the determination of additives on polymeric surfaces. The classical methods of... 

Advanced techniques like molecularly imprinted polymers (MIPs), infrared/near infrared spectroscopy (FT-IR/NIR), high resolution mass spectrometry, nuclear magnetic resonance (NMR), Raman spectroscopy, and biosensors will increasingly be applied for controlling food quality and safety. 

The formal approach of 2D correlation analysis to time-dependent spectral intensity fluctuations has been extended to UV, Raman [1010], and near-IR spectroscopy [1011-1014] 2D fluorescence is upcoming. 

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