Identification Raman spectroscopy

Other Inorganics. Inorganic species in solution have been studied very effectively by Raman spectroscopy. Work in this area includes the investigation of coordination compounds (qv) of fluorine (qv) (40), the characterization of low dimensional materials (41) and coordinated ligands (42), and single-crystal studies (43). Several compilations of characteristic vibrational frequencies of main-group elements have been pubflshed to aid in the identification of these species (44,45). 

Raman spectroscopy, long used for quaHtative analysis, has been revitalized by the availabiHty of laser sources. Raman spectroscopy is based on scattering of light with an accompanying shift in frequency. The amount by which the frequency is shifted is characteristic of the molecules that cause the scattering. Hence, measurement of the frequency shift can lead to identification of the material. 

Materials characterization techniques, ie, atomic and molecular identification and analysis, ate discussed ia articles the tides of which, for the most part, are descriptive of the analytical method. For example, both iaftared (it) and near iaftared analysis (nira) are described ia Infrared and raman SPECTROSCOPY. Nucleai magaetic resoaance (nmr) and electron spia resonance (esr) are discussed ia Magnetic spin resonance. Ultraviolet (uv) and visible (vis), absorption and emission, as well as Raman spectroscopy, circular dichroism (cd), etc are discussed ia Spectroscopy (see also Chemiluminescence Electho-analytical techniques It unoassay Mass specthot thy Microscopy Microwave technology Plasma technology and X-ray technology). 

Infrared (in) spectrometers are gaining popularity as detectors for gas chromatographic systems, particularly because the Fourier transform iafrared (ftir) spectrometer allows spectra of the eluting stream to be gathered quickly. Gc/k data are valuable alone and as an adjunct to gc/ms experiments. Gc/k is a definitive tool for identification of isomers (see Infrared and raman spectroscopy). 

Raman spectroscopy is a very convenient technique for the identification of crystalline or molecular phases, for obtaining structural information on noncrystalline solids, for identifying molecular species in aqueous solutions, and for characterizing solid—liquid interfaces. Backscattering geometries, especially with microfocus instruments, allow films, coatings, and surfaces to be easily measured. Ambient atmospheres can be used and no special sample preparation is needed. 

The yellow disulfide radical anion and the briUiant blue trisulfide radical anion often occur together for what reason some authors of the older Hterature (prior to 1975) got mixed up with their identification. Today, both species are well known by their E8R, infrared, resonance Raman, UV-Vis, and photoelectron spectra, some of which have been recorded both in solutions and in solid matrices. In solution these radical species are formed by the ho-molytic dissociation of polysulfide dianions according to Eqs. (7) and (8). 8ince these dissociation reactions are of course endothermic the radical formation is promoted by heating as well as by dilution. Furthermore, solvents of lower polarity than that of water also favor the homolytic dissociation. However, in solutions at 20 °C the equilibria at Eqs. (7) and (8) are usually on the left side (excepting extremely dilute systems) and only the very high sensitivity of E8R, UV-Vis and resonance Raman spectroscopy made it possible to detect the radical anions in liquid and solid solutions see above. 

High performance spectroscopic methods, like FT-IR and NIR spectrometry and Raman spectroscopy are widely applied to identify non-destructively the specific fingerprint of an extract or check the stability of pure molecules or mixtures by the recognition of different functional groups. Generally, the infrared techniques are more frequently applied in food colorant analysis, as recently reviewed. Mass spectrometry is used as well, either coupled to HPLC for the detection of separated molecules or for the identification of a fingerprint based on fragmentation patterns. ... 

In 1994, we proposed that a metallic needle having a nano-tip at its apex be employed as a nano-light-source for microscopy attaining nanometric spatial resolution [2]. Later, we expanded the technique to Raman spectroscopy for molecular nano-identification, nano-analysis and nano-imaging. In this chapter, we give a brief introduction to local plasmons and microscopy using a metallic nano-needle to produce the local plasmons. Then, we describe the microscope that we built and... 

A nano-light-source generated on the metallic nano-tip induces a variety of optical phenomena in a nano-volume. Hence, nano-analysis, nano-identification and nanoimaging are achieved by combining the near-field technique with many kinds of spectroscopy. The use of a metallic nano-tip applied to nanoscale spectroscopy, for example, Raman spectroscopy [9], two-photon fluorescence spectroscopy [13] and infrared absorption spectroscopy [14], was reported in 1999. We have incorporated Raman spectroscopy with tip-enhanced near-field microscopy for the direct observation of molecules. In this section, we will give a brief introduction to Raman spectroscopy and demonstrate our experimental nano-Raman spectroscopy and imaging results. Furthermore, we will describe the improvement of spatial resolution... 

The identification of surface adsorbed species has been carried out with FT-IR [69] and Raman spectroscopy [70] during reaction and with GC-MS after epoxidation reaction [72]. The aggregation of gold NPs is not appreciable during reaction at temperatures below 473 K [69,72]. Catalyst deactivation, which happens within a few hours causing a decrease in C3FI6 conversion by about 50%, can be accounted for by the accumulation of successively oxidized compounds after isomerization and cracking of... 

In summary, the combined experimental (NIS, IR- and Raman-spectroscopy) and computational (DFT) approach has enabled the identification of the vibrational modes that contribute most to the entropic driving force for SCO transition. 

Raman spectroscopy has been used for a long time in order to study supported and promoted metal catalysts and oxide catalysts [84] since many information can be obtained (1) identification of different metal oxide phases (2) structural transformations of metal oxide phases (3) location of the supported oxide on the oxide substrate and... 

The identification of xanthophylls in vivo is a complex task and should be approached gradually with the increasing complexity of the sample. In the case of the antenna xanthophylls, the simplest sample is the isolated LHCII complex. Even here four xanthophylls are present, each having at least three major absorption transitions, 0-0, 0-1, and 0-2 (Figure 7.4). Heterogeneity in the xanthophyll environment and overlap with the chlorophyll absorption add additional complexity to the identification task. No single spectroscopic method seems suitable to resolve the overlapping spectra. However, the combination of two spectroscopic techniques, low-temperature absorption and resonance Raman spectroscopy, has proved to be fruitful (Ruban et al., 2001 Robert et al., 2004). 

Raman spectroscopy allows chemical identification of single phases and in the imaging mode a description of the morphology. Raman bands characteristic of the two main components PA and PTFE are easily distinguishable, as shown in Figure 6, where pure materials have been used from which to record reference spectra. To identify PTFE in the spectra of the bearing the symmetric C-F... 

Pure pigments and dyes can be identified from their IR spectrum. Some reference spectra are given in the Hummel and Scholl collection [9]. Other than simple white pigments or solvent soluble types, identification of pigments in finished products is particularly difficult. Raman spectroscopy can aid the positive identification of pigments such as titanium dioxide. 

Most chemists tend to think of infrared (IR) spectroscopy as the only form of vibrational analysis for a molecular entity. In this framework, IR is typically used as an identification assay for various intermediates and final bulk drug products, and also as a quantitative technique for solution-phase studies. Full vibrational analysis of a molecule must also include Raman spectroscopy. Although IR and Raman spectroscopy are complementary techniques, widespread use of the Raman technique in pharmaceutical investigations has been limited. Before the advent of Fourier transform techniques and lasers, experimental difficulties limited the use of Raman spectroscopy. Over the last 20 years a renaissance of the Raman technique has been seen, however, due mainly to instrumentation development. 

Raman spectroscopy is emerging as a powerful analytical tool in the pharmaceutical industry, both in PAT and in qualitative and quantitative analyses of pharmaceuticals. Reviews of analyses of pharmaceuticals by Raman spectroscopy have been published.158 159 Applications include identification of raw materials, quantification of APIs in different formulations, polymorphic screening, and support of chemical development process scale-up. Recently published applications of Raman spectroscopy in high-throughput pharmaceutical analyses include determination of APIs in pharmaceutical liquids,160,161 suspensions,162 163 ointments,164 gel and patch formulations,165 and tablets and capsules.166-172... 

Dong J, Cheng Z, Zha S, and Liu M. Identification of nickel sulfides on Ni-YSZ cermet exposed to H2 fuel containing H2S using Raman spectroscopy. J Power Sources 2006 156 461 165. 

The use of surface-enhanced resonance Raman spectroscopy (SERRS) as an identification tool in TLC and HPLC has been investigated in detail. The chemical structures and common names of anionic dyes employed as model compounds are depicted in Fig. 3.88. RP-HPLC separations were performed in an ODS column (100 X 3 mm i.d. particla size 5 pm). The flow rate was 0.7 ml/min and dyes were detected at 500 nm. A heated nitrogen flow (200°C, 3 bar) was employed for spraying the effluent and for evaporating the solvent. Silica and alumina TLC plates were applied as deposition substrates they were moved at a speed of 2 mm/min. Solvents A and B were ammonium acetate-acetic acid buffer (pH = 4.7) containing 25 mM tributylammonium nitrate (TBAN03) and methanol, respectively. The baseline separation of anionic dyes is illustrated in Fig. 3.89. It was established that the limits of identification of the deposited dyes were 10 - 20 ng corresponding to the injected concentrations of 5 - 10 /ig/ml. It was further stated that the combined HPLC-(TLC)-SERRS technique makes possible the safe identification of anionic dyes [150],... 

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