Structure identification using Raman spectroscopy

Clark et al, (1969) Clark, J.R. Appleman, D.E. Papike, J.J. Crystal-chemical characterization of clinopyroxenes based on eight new structure refinements Mineralogical Society of America Special Papers 2 (1969) 31-50 Clark et al (1995) Clark, R.J.H. Synthesis, structural characterization and Raman spectroscopy of the inorganic pigments lead tin yellow types I and II and lead antimonate yellow their identification on Medieval paintings and manuscripts Journal of the Chemical Society. Dalton Transactions 16 (1995) 2577-2582 Clarke (1976) Clarke, J. Two Aboriginal rock art pigments from Western Australia their properties, use and durability Studies in Conservation 21 (1976) 134-142, 159-160... 

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. 

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 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],... 

In the geosciences Raman spectroscopy has traditionally been a laboratory tool for structural analysis of minerals. Recent developments in instrumentation make possible the use of Raman spectroscopy as a tool for routine identification of minerals in field situations. The following advantages characterize Raman analysis of minerals no sample preparation in situ real time measurement non-destructive and non-intrusive sampling samples may be transparent or opaque spectra are well resolved and with high information content. 

The Raman spectra of a-lactose monohydrate, /1-lactose in the crystalline state, a-lactose-/3-lactose mixture, and equilibrated lactose in aqueous solution have been investigated.186 It was found that the spectra are very sensitive to small structural changes, and this suggested that Raman spectroscopy should be used as a method for identification of closely related isomers. 

Raman spectroscopy can be used in qualitative and quantitative measurements of both organic and inorganic materials, and it is successfully employed to solve complex analytical problems such as determining chemical structures. Gases, vapors, aerosols, liquids, and solids can be analyzed by spectroscopy. As well as room temperature observations, cryogenic and high-temperature measurements can be made, including in situ identification and quantification of combustion products in flames and plasmas (Laserna, 1996). 

Raman spectroscopy is by no means a new technique, although it is not as widely known or used by chemists as the related technique of infrared spectroscopy. However, following developments in the instrumentation over the last 20 years or so Raman spectroscopy appears to be having something of a rebirth. Raman, like infrared, may be employed for qualitative analysis, molecular structure determination, functional group identification, comparison of various physical properties such as crystallinity, studies of molecular interaction and determination of thermodynamic properties. 

In general, Raman spectroscopy has been used very little, if at all, to perform quantitative analyses its primary use has been in the study of molecular structure. However, one possible use of laser Raman spectroscopy for quantitative purposes is the identification and determination of trace levels of molecular pollutants in water [10]. The Raman spectrum of distilled water is weak and uncomplicated thus it is possible to detect and distinguish Raman bands of pollutants in natural waters. For example, it is possible to detect as little as 50 ppm of benzene in distilled water using only 5 mW of laser power from a He-Ne gas laser at 6328 A. With improved excitation techniques and 50 mW laser power, it should be possible to detect certain Raman-active pollutants at less than 5 ppm levels. 

A combination of Raman and Si MAS NMR spectroscopy was employed by Annen and Davis [280] for a structure investigation of framework materials containing three-membered rings (3MR) including molecular sieves such as lovdarite, ZSM-18 and VPI-8. However, it turned out that Raman spectroscopy is not useful for the identification of three-membered rings in framework materials. 

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