Identification Raman techniques

Bussotti L., Castellucci E., Matteini M., The Micro-Raman Technique in the Studies for the Conservation of Art Works Identification of Lakes in Paints, Science and Technology for Cultural Heritage 1996 5 (1) 13. 

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. 

A significant contribution of Raman spectroscopy to the analytical characterization of biomedical issues has been made in the area of biomaterials, especially in the identification of biodegradation and deterioration [1, 2]. The general impact of Raman spectroscopy on the study of biomaterials has been described by this author in three recent review articles [3-5]. In this chapter, the topic of Raman characterization of biomaterials is revisited with particular emphasis placed on those biomaterials widely employed for load-bearing surfaces in artificial joints. Important recent case studies are presented to illustrate the power of the Raman technique to answer key questions of broad medical, scientific, and technological interest. The analytical and physical science lying behind the Raman effect is shown to contribute to the accumulation of a wealth of fundamental information about the medical and technical achievements of prosthesis makers. 

Since IR spectroscopy is a standard, and perhaps currently the most widely used tool in the search for and characterization of polymorphs, there are likely to be thousands of references to the use of the technique in connection with polymorphs. The vast majority of these deal with the determination of the IR fingerprint of a polymorphic modification. In this section, we wish to note a few cases in which the IR and Raman techniques were employed to obtain chemical information somewhat beyond the mere identification of a particular crystal modification. For instance, Mathieu (1973) showed for a number of chiral compounds that it is possible to distinguish between a dl racemate and a conglomerate of d and / crystals by use of IR and/or Raman spectroscopy, even when it may not be possible to make such a distinction by physical or visual means. 

Because Raman spectmm stems from the bonds vibrations, it provides an intrinsic nano-probing and offers a bottom-up approach of nanostmctured materials that comes as a good complement to other techniques such as transmission electron microscopy. X-ray diffraction, and infrared, and Mossbauer spectroscopy. Since almost no sample preparation is needed, Raman technique [12, 13] is commonly used to investigate nanomaterials. This could provide the phase identification and, possibly, size estimation [14]. 

The X-ray diffraction patterns for Ge02 (H) and Ge02 (T) have been accurately determined and can be used to identify films as thin as 500 A (using low angle diffraction). Here again, the monoxide phase cannot be identified by this means since no diffraction pattern has been observed for that phase. Some other non-destructive techniques have been used such as low energy electron diffraction (LEED), electron loss spectroscopy (ELS), Raman scattering, etc. but usually they are so sensitive to contamination that the results cannot easily be used for simple phase identification. Such techniques are therefore more useful for physical property studies. 

The ability to ID black plastics is of secondary importance in the case of bottles but becomes more important for some electrical and electronic plastics and for many automotive plastics. Mid-infrared (MIR) can identify many black plastics but not near-infrared (NIR), where the carbon black interferes [19, 64, 65]. Recently, a company has reported success in applying laser Raman techniques to the rapid identification of black plastics [66]. 

Infrared (IR) and Raman are both well established as methods of vibrational spectroscopy. Both have been used for decades as tools for the identification and characterization of polymeric materials in fact, the requirement for a method of analysis synthetic polymers was the basis for the original development of analytical infrared instrumentation during World War II. It is assumed that the reader has a general understanding of analytical chemistry, and a basic understanding of the principles of spectroscopy. A general overview of vibrational spectroscopy is provided in Sec. 5 for those unfamiliar with the infrared and Raman techniques. 

Prior to the much-vaunted renaissance of the Raman technique with the advent of FT instrumentation or the availability of CCD systems, there were few literature reports on the use of Raman spectroscopy for investigating pharmaceutical systems. The technique has been used to characterize drugs in much the same way that infrared has been used for identification testing. Thus, the infrared (IR) and Raman spectra of Dapsone, used in the treatment of leprosy, have been reported [1]. 

The determination of the spatial distribution of chemical species in polymeric systems is perhaps the most basic and most commonly encountered use of microspectroscopy. This technique is frequently used for the identification of defects in finished polymer products and for the identification of phase-separated regions of polymer blends. Polymer laminate films, which typically consist of layers between 2 and 10 iLim thick, are also frequently studied using this technique. Raman techniques are typically more useful than IR... 

The purpose of this chapter is to help those interested in the characterisa-tion/identification of biological molecules/samples. The intention is not to deal with infrared or Raman techniques, nor to deal with sampling methods for the two techniques. There are several good books dealing with these aspects. 

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). 

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. 

Thus, a more complete study of the spectral properties and the structure of intermediates frozen in inert matrices is achieved when the IR, Raman, UV and esr spectroscopic methods are mutually complementary. Since IR spectroscopy is the most informative method of identification of matrix-isolated molecules, this review is mainly devoted to studies which have been performed using this technique. 

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... 

Since SERS and SERRS are substance specific, they are ideal for characterisation and identification of chromatographically separated compounds. SE(R)R is not, unfortunately, as generally applicable as MS or FUR, because the method requires silver sol adsorption, which is strongly analyte-dependent. SE(R)R should, moreover, be considered as a qualitative rather than a quantitative technique, because the absolute activity of the silver sol is batch dependent and the signal intensity within a TLC spot is inhomogeneously distributed. TLC-FTIR and TLC-RS are considered to be more generally applicable methods, but much less sensitive than TLC-FT-SERS FT-Raman offers p,m resolution levels, as compared to about 10p,m for FTIR. TLC-Raman has been reviewed [721],... 

The use of Raman microscopy in the detection and identification of pigments on manuscripts, paintings, ceramics and papyri was reviewed by Clark (1999). He concludes that it is arguable the best single technique to be applied to this area, since it combines the attributes of reproducibility and sensitivity with those of being nondestructive and immune to interference from both pigments and binders. He points... 

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