Probe Raman spectrometry

Water soluble synthetic polyelectrolytes have attracted increasing attention in recent years, mainly because of their wide utility in industrial applications, and also because of their resemblance to biopolymers. PolyCmethacrylic acid), PMA, a wea)c polyelectrolyte, exhibits a mar)ced pH induced conformational transition. A wide variety of techniques have been employed to gain more information on the nature of the conformational transition of PMA, these techniques include viscometry, potential titrimetry,(1-5) Raman spectrometry,(6) calorimetry,(7-9) electrical conductometry,(10) dilatometry,(11) H NMR linewidth,(12) viscoelastic studies,(13) )cinetics of chemical reactions, (14) small-angle neutron scattering,(15) pH jump,(16,17) and fluorescent probing.(18-27)... 

The end product of the hydrosilylation reaction is mixed with an exact amount of the Si-H-containing educt (6 samples). These samples are analyzed in parallel by H NMR and an FT-Raman spectrometry probe head which is connected to the spectrometer via a fiber optical cable. For the FT-Raman measurement, the same parameters are used which will be used later for the real measurement, e.g., measuring time 60 s and background measming before every measurement. 

One of the significant advantages of Raman spectrometry is that it is based on visible or near-IR radiation that can he transmitted lor a considerable distance (as much as 100 m or more) through optical fibers. Figure 18-9 shows the arrangement of a typical Raman instrument that uses a fiber-optic probe. Here, a microscope objective lens is used to focus the laser excitation beam on one end of an excitation liber of a fiber bundle. These libers bring the excitation radiation to the sample. I ibers can be immersed in liquid samples or used to illuminate solids. A second fiber or liber bundle collects the Raman scattering and transports it to... 

IR Lewis, ML Lewis. Fiber optic probes for Raman spectrometry. In J Chalmers, PR Griffiths, eds. Handbook of Vibrational Spectroscopy. Chichester Wiley, 200, vol. 2. 

RL McCreery, M Fleischmann, P Hendra. Fiber optic probe for remote Raman spectrometry. Anal Chem 55 146-148, 1983. 

Infrared and ultraviolet probes for surface analysis are then considered.The applications of IR spectroscopy and Raman microscopy are discussed, and a brief account is also given of laser-microprobe mass spectrometry (LAMMA). 

One problem with methods that produce polycrystalline or nanocrystalline material is that it is not feasible to characterize electrically dopants in such materials by the traditional four-point-probe contacts needed for Hall measurements. Other characterization methods such as optical absorption, photoluminescence (PL), Raman, X-ray and electron diffraction, X-ray rocking-curve widths to assess crystalline quality, secondary ion mass spectrometry (SIMS), scanning or transmission electron microscopy (SEM and TEM), cathodolumi-nescence (CL), and wet-chemical etching provide valuable information, but do not directly yield carrier concentrations. 

Weckhuysen and coworkers (Nijhuis et al., 2003) described equipment suitable for parallel Raman and UV-vis spectroscopic measurements. Openings on the opposite sides of a furnace allowed acquisition of Raman and UV-vis spectra through optical grade windows in a tubular quartz reactor. UV-vis spectra were recorded at 823 K. Gas-phase analysis was achieved with mass spectrometry and gas chromatography. A more advanced version of the design (Nijhuis et al., 2004) accommodates four optical fiber probes, placed at 10-mm vertical spacing along the tubular reactor. The temperature that the fibers can withstand is 973 K the reported spectra characterize samples at 823 K. 

XRD, X-ray diffraction XRF, X-ray fluorescence AAS, atomic absorption spectrometry ICP-AES, inductively coupled plasma-atomic emission spectrometry ICP-MS, Inductively coupled plasma/mass spectroscopy IC, ion chromatography EPMA, electron probe microanalysis SEM, scanning electron microscope ESEM, environmental scanning electron microscope HRTEM, high-resolution transmission electron microscopy LAMMA, laser microprobe mass analysis XPS, X-ray photo-electron spectroscopy RLMP, Raman laser microprobe analysis SHRIMP, sensitive high resolution ion microprobe. PIXE, proton-induced X-ray emission FTIR, Fourier transform infrared. 

Transient intermediates are most commonly observed by their absorption (transient absorption spectroscopy see ref. 185 for a compilation of absorption spectra of transient species). Various other methods for creating detectable amounts of reactive intermediates such as stopped flow, pulse radiolysis, temperature or pressure jump have been invented and novel, more informative, techniques for the detection and identification of reactive intermediates have been added, in particular EPR, IR and Raman spectroscopy (Section 3.8), mass spectrometry, electron microscopy and X-ray diffraction. The technique used for detection need not be fast, provided that the time of signal creation can be determined accurately (see Section 3.7.3). For example, the separation of ions in a mass spectrometer (time of flight) or electrons in an electron microscope may require microseconds or longer. Nevertheless, femtosecond time resolution has been achieved,186 187 because the ions or electrons are formed by a pulse of femtosecond duration (1 fs = 10 15 s). Several reports with recommended procedures for nanosecond flash photolysis,137,188-191 ultrafast electron diffraction and microscopy,192 crystallography193 and pump probe absorption spectroscopy194,195 are available and a general treatise on ultrafast intense laser chemistry is in preparation by IUPAC. 

Two final checks should be performed. Following quantitation, the identity of the evolved gas should be established using appropriate methods (mass spectrometry, infrared or Raman spectroscopy, etc.). The solid residue in the reactor from the oxidation should also be probed with vibrational and/or NMR spectroscopy to establish that none of the ligand of interest remains. In the event that some ligand remains following oxidation, quantitation of the ligand of interest is still possible if the identity and yield of the oxidized compound can be established. 

Field emission scanning electron microscopy (FESEM), glancing incidence x-ray diffraction (GIXRD), transmission electron microscopy (TEM), micro Raman scattering, Fourier transform inftaied (FTIR) spectrometry, Rutherford back scattering (RBS) studies and electron probe micro analysis (EPMA) have been carried out to obtain micro-structural and compositional properties of the diamond/p-SiC nanocomposite films. Atomic force microscopy (AFM) and indentation studies have been carried out to obtain film properties on the tribological and mechanical front. 

Outside of absorbance and fluorescence, microchip CL systems will become more common, likely using ECL with in situ regenerated lumophores. Will the next decades finally witness the commercial development of a capillary-scale Raman probe Of course, the continued hyphenation of UV-absorbance, mass spectrometry, and other detection schemes will push the envelope of information-rich detection systems for small-volume separations. 

Chemical reactions at the gas-surface interface can be followed by monitoring gas-phase products with, for example, a mass spectrometer, or by directly analyzing the surface with a spectroscopic technique such as Auger electron spectroscopy (AES), photoelectron spectroscopy (PES), or electron energy loss spectroscopy (EELS), all of which involve energy analysis of electrons, or by secondary ionization mass spectrometry (SIMS), which examines the masses of ions ejected by ion bombardment. Another widely used surface probe is low-energy electron diffraction (LEED), which can provide structural information via electron diffraction patterns. At the gas-liquid interface, optical reflection elHpsometry and optical spectroscopies are employed, such as Eourier transform infrared (ET IK) and laser Raman spectroscopies. 

Although a combination of spectroscopy imaging e.g. /xXRF, /xFTIR, /xRS) would offer a powerful way to characterise materials various hurdles must be overcome to achieve the ultimate in integrated spectroscopic imaging. These difficulties include spatial resolution, specimen preparation, spectroscopic probe penetration depth and image integration. Same-spot (optical, /u-FTIR, /u.RS) technology is now available. The topic of Raman microscopy in combination with other microanalysis techniques (electron microscopy/X-ray microanalysis ion mi-croprobe mass spectrometry, and laser microprobe mass spectrometry), i.e. dual-use microprobe systems, has been discussed [534]. 

In principle, all kinds of spectroscopic techniques lend themselves to on-line measurements. Only a very few are practical. Although low-field NMR has been used to measure various material properties by applying empirical relationships, NMR is still not a realistic proposition for on-line measurements. Ironically, ETIR spectroscopy suffers from too much sensitivity. Typically, good spectra can be obtained only from very thin polymeric films (or solutions). Attenuated total reflection (ATR) probes, in which only a fraction of the IR light penetrates a very short distance into the sample, reduce the problem of excessive sensitivity. However, they aggravate the problems of variations in the baseline and nonlinear response. The latter problem also obstructs the use of UV spectrometry for monitoring polymerization reactions. Of the remaining options, near-infrared (NIR) and Raman spectroscopy are the most attractive. 

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