Samples Raman

Resonance Raman spectroscopy has been applied to studies of polyenes for the following reasons. The Raman spectrum of a sample can be obtained even at a dilute concentration by the enhancement of scattering intensity, when the excitation laser wavelength is within an electronic absorption band of the sample. Raman spectra can give information about the location of dipole forbidden transitions, vibronic activity and structures of electronically excited states. A brief summary of vibronic theory of resonance Raman scattering is described here. 

For smaller samples, Raman spectra can be collected through a microscope. Process microspectroscopy systems, such as might be used for semiconductor chip manufacturing or pharmaceutical high throughput... 

To use Raman scattering as a method of isolating the orientation of the individual blocks of the sample, Raman scattering spectra were examine to ensure that each block yielded separate, identifiable peaks. For the PS-PBD system, these are provided by the C-C aromatic-aliphatic stretching vibration of the PS at a frequency of 1029 cm-1, and at... 

The limitations of Raman spectroscopy are its low sensitivity compared to IR absorption and fluorescence interference from impurities in the sample. Raman spectroscopy is a developing technology, and a good amount of research and planning is necessary before deciding whether or not to employ it. The cost of a Raman process analyzer exceeds that of other analyzers. To reduce cost, Raman analyzers often include multichannel capability. Up to four process streams can be analyzed with a single CCD camera by splitting the lasers. 

Raman Spectroscopy provides information comparable to that obtained by FTIR. The sample is illuminated by a laser beam (visible light), and the light dispersed from the sample (Raman effect) [46] is analyzed. The frequency differences between the light dispersed and that of the initial laser beam reflect the various functional groups of surface and solution species. This method can also be used... 

Raman scatter can also be troublesome. Depending on the wavelength pair of the sample, Raman scatter from the mobile phase can overlap the fluorescence... 

In the case of pharmaceutical samples, Raman spectroscopy is sensitive to crystallinity and polymorphism, both of which are important with regards to the bioavailability (and protection of the intellectual property) of active ingredients. 

Raman spectroscopy has a number of benefits for process analysis applications. For appropriate samples Raman spectra are rich in information content Figure 17.5 shows the superimposed Raman spectra of pentane, hexane, heptane and octane which can be compared with the corresponding NIR spectra in Fig. 17.4. The spectra and resultant information are similar to those obtained from mid-IR. 

Raman scatter can also be troublesome. Depending on the wavelength pair of the sample, Raman scatter from the mobile phase can overlap the fluorescence signal and, thus, can be misdiagnosed as the fluorescence signal itself. This problem arises during increasing instrument sensitivity. However, satisfactory separation can be achieved by... 

Vibrational spectroscopy is a vitally important technique in inorganic chemistry, used both to identify new and known compounds, and to check the purity of samples. Infrared (IR) spectrometers are widely available and are relatively cheap, so IR spectroscopy is normally one of the first techniques to be used when studying a new sample. Raman spectrometers have also become more routinely used in recent years, and have the advantage that they can focus on tiny specimens. 

Raman spectroscopy is widely used as a diagnostic tool for the evaluation of diamond crystals and CVD diamond films. The technique is popular because each carbon allotrope displays a clearly identifiable Raman signature, it is nondestructive (when the correct laser irradiation parameters are chosen), requires little or no specimen preparation, and can be made confocal so that micrometer volumes can be sampled. Raman scattering from single-crystal, CVD diamond films, and ND has recently been reviewed in Refs. 87,88. 

Raman spectroscopy has already been realized to be an important analysis tool for me-teoritic and lunar samples. In lunar samples, Raman has been used to identify minerals present [73] and their proportions [74]. The degree of shock of olivine in L6 chondrites... 

Figure 7 Effect of window position on the observed optic background for an opaque latex sample. Raman spectra of latex obtained with (a) a X10 objective, (b) an immersion optic focused close to the window surface, and (c) an immersion optic focused into the sample, and (d) the Raman spectrum of the sapphire window 785-nm excitation. Note that bands marked with an asterisk originate from the sapphire window. 

Sensitivity depends on the relative intensities of the analyte Raman bands compared with overlapping, interfering Raman bands and emissions from the sample. Raman analysis is often hindered by fluorescence by the sample or impurities with the laser excitation line being used. Fluorescence occurs when the excitation line is partially absorbed and reemitted. The quantum yield of the fluorescence process is often several orders of magnitude higher than that of the Raman process, and thus any useful spectroscopic information is lost, cfr. Fig. 1.19). Fluorescence interference does not normally occur in condensed phases with UV excitation wavelengths below 260 nm [357]. There is no single solution to the fluorescence problem in Raman spec-... 

In terms of axial resolution, for transparent samples, Raman microscopy is governed by the focal depth of the objective, whereas IR microscopy is governed by the thickness of the sample (in simple transmission mode). For a 100 x objective, this is typically 1-2 pm and the axial resolution can be improved by taking advantage of confocal imaging conditions. An important consideration, however, is that whereas in the visible region the majority of cellular... 

Abstract. Recent years have seen a growing interest in the use of Raman-based spectroscopy as an analytical tool for the chemical analysis of biological samples. Raman spectroscopy has found many applications in cellular and structural biology, biomedicine, and biodetection. Its attractiveness for live biological studies lies mainly in its hi sensitivity to molecular interactions and small molecular scale conformational changes. In addition, the noninvasiveness of this s roach permits both in-vitro and in-vivo studies. This increased interest has been a result of advances in both instrumentation and techniques that have enabled improved data acquisition and data interpretation. This chapter addresses recent advances in Raman-based techniques and highlights their uses in specific biological studies. 

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