Raman sample preparation

Raman sample preparation. A fine powder was preparable by shaking the solid in the reaction tube at — 78°C. These powders gave the Raman spectrum represented in Figure 3 and the X-ray powder pattern given in Table IV. 

Sample preparation is straightforward for a scattering process such as Raman spectroscopy. Sample containers can be of glass or quartz, which are weak Raman scatterers, and aqueous solutions pose no problems. Raman microprobes have a spatial resolution of - 1 //m, much better than the diffraction limit imposed on ir microscopes (213). Eiber-optic probes can be used in process monitoring (214). 

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. 

Recent developments in Raman equipment has led to a considerable increase in sensitivity. This has enabled the monitoring of reactions of organic monolayers on glassy carbon [4.292] and diamond surfaces and analysis of the structure of Lang-muir-Blodgett monolayers without any enhancement effects. Although this unenhanced surface-Raman spectroscopy is expected to be applicable to a variety of technically or scientifically important surfaces and interfaces, it nevertheless requires careful optimization of the apparatus, data treatment, and sample preparation. 

Minimal sample preparation is involved in Raman spectroscopy samples as thin as a monolayer can be examined. 

The goal of our investigations was to characterise the morphology of the sample, and to determine the size and location of the PTFE and silicone oil phases by different methods [46,47], For phase characterization using Raman microscopy, no special sample preparation was necessary. For FTIR imaging, microtomed sections (5 pm in thickness) had to be prepared by cutting the sample with a diamond knife at — 80°C ("cryo-microtomy") to prevent smearing and to obtain flat surfaces. 

Raman microscopy provides a spatial resolution slightly better than IR, and no sample preparation is necessary in many cases. It has advantages with special types of substances (e.g., systems containing conjugated double bonds, oriented systems, amorphous and crystalline carbon, oxides). SNOM techniques (with spatial resolution below 1 pm) have been more popular with Raman than with IR, so far, but as yet are not routinely practiced. 

Raman spectroscopy is one of the most powerful techniques for the characterization of nanocarbons. It is also a convenient technique because it involves almost no sample preparation and leaves the material unharmed. There are four characteristic bands for CNTs The band at 200 cm-1 is called radial breathing mode (RBM). It depends on the curvature and can be used to calculate the diameter of SWCNTs [61]. The relatively broad D-band at 1340 cm-1 is assigned to sp2-related defects and disorder in the graphitic structure of the material. The tangential C-C stretching mode is located at -1560 cm 1 (G-band). The second order mode of the D-band can be observed (G -band,... 

Raman samples were prepared by peeling SiNW thin films off the silicon wafers to avoid Raman signals from the silicon substrate. A razor blade was used to shave the thin films on top of the silicon wafers. The thin films were mounted on a carbon tape for SEM and Raman inspection, or on a transparent Mylar film for Raman measurements. 

Natural products, from plants and foods to rocks and minerals, are complicated systems, but their analysis by Raman spectroscopy is a growing area. Most examples come from quality control laboratories, motivated to replace current time-consuming sample preparation and analysis steps with a less labor-intensive, faster technique but most authors anticipated the eventual application to process control. Often a method will be practiced in a trading house or customs facility to distinguish between items perceived to be of different qualities, and thus prices. 

NIR Vibrational overtones and combination bands Very high S/N Relatively low sensitivity facilitates minimum sample preparation Most popular on-line technique, but not as sensitive or diagnostic as IR and Raman. Sensitivity to physical as well as chemical status can be a problem or an opportunity, depending on application... 

In this review, the vibrational spectra of solid chalcogenometallates are presented and a critical discussion of the results given. Initially, measurements of powdered, crystalline samples with isolated ions or molecules are presented followed by single crystal Raman studies which are rarer. Additionally, a group of topics including the interpretation of Raman band intensities and widths. Resonance Raman spectra, the influence of pressure, temperature and sample preparation will be discussed. 

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. 

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 limit of detection by Raman spectroscopy was 3-5 weight % for the oxime ester and methacrylonitrile for these samples. The shorter time required to reduce background fluorescence in those samples filtered through activated charcoal indicates that more careful sample preparation and purification would lower this limit. 

Raman spectroscopy is a non-destructive technique that is used in cosmochemistry for identification of minerals and to evaluate the bonding and composition of organic molecules. The technique does not require special sample preparation raw rock samples, polished sections, fine-grained powders, and liquids can be analyzed. Raman spectroscopy is the basis for several instruments that are under consideration for upcoming NASA missions. 

There are advantages in the Raman field over its absorption counterpart. Thus, many of the functional groups which, due to their very high (dfijdq) values, tend to obscure the infrared spectrum (e.g. vC-O-, vC-F, vO-H and <50-H) rarely give any trouble in this respect in the Raman effect. Those familiar with the infrared spectrum of poly-(tetra-fluoro ethylene) or of polyoxymethylene will confirm this when they compare their data with Fig. 10 and 11, respectively. In addition, all the spectra given in this review were recorded on readily available samples — with no sample preparation. 

For formulated products an essential analysis is the assay for API content. This is usually performed by HPLC, but Raman spectroscopy can offer a quantitative analytical alternative. These applications have been extensively researched and reviewed by Strachan et al. [48] and provide over 30 literature references of where Raman spectroscopy has been used to determine the chemical content and physical form of API in solid dosage formulations. As no sample preparation is required the determination of multiple API forms (e.g. polymorphs, hydrates/solvates and amorphous content) provides a solid state analysis that is not possible by HPLC. However, as previously discussed sampling strategies must be employed to ensure the Raman measurement is representative of the whole sample. A potential solution is to sample the whole of a solid dosage form and not multiple regions of it. As presented in Chap. 3 the emerging technique of transmission Raman provides a method to do just this. With acquisition times in the order of seconds, this approach offers an alternative to HPLC and NIR analyses and is also applicable to tablet and capsule analysis in a PAT environment. 

Raman spectroscopy can offer a number of advantages over traditional cell or tissue analysis techniques used in the field of TE (Table 18.1). Commonly used analytical techniques in TE include the determination of a specific enzyme activity (e.g. lactate dehydrogenase, alkaline phosphatase), the expression of genes (e.g. real-time reverse transcriptase polymerase chain reaction) or proteins (e.g. immunohistochemistry, immunocytochemistry, flow cytometry) relevant to cell behaviour and tissue formation. These techniques require invasive processing steps (enzyme treatment, chemical fixation and/or the use of colorimetric or fluorescent labels) which consequently render these techniques unsuitable for studying live cell culture systems in vitro. Raman spectroscopy can, however, be performed directly on cells/tissue constructs without labels, contrast agents or other sample preparation techniques. 

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