Spectral acquisition

In order to more accurately identify the contaminant, and to determine if the fuel delivery system module filter was the source, both materials were analyzed using 1H NMR spectroscopy Samples were dissolved in a 60 40 mixture of deuterated chloroform/triflouroethanol. It should be noted that the amount of contaminant available for analysis was quite small, so for this sample, the NMR spectral acquisition time was set to 1 h in order to record a spectrum of adequate signal-to-noise ratio. 

Fig. 7 Thermogravimetric weight loss curve (A) and subsequent IR spectra measured at the designated temperatures (B) 70°C, (C) 95°C, (D) 120°C, (E) 160°C, and (F) 180°C. A slight lag time exists between the TG weight loss and IR spectral acquisition due to the evolved gas being carried into the IR gas cell by the He carrier gas. Each IR spectrum is plotted on the same absolute intensity scale (Abs. units).

In the frequency region where the i/(0H) vibrations of interfacial H20 are observed, the normal Raman scattering from the bulk solution can obscure the SERS of interfacial H20 if appropriate precautions are not taken. In the studies reported here, the SERS of interfacial H20 was acquired with the electrode surface positioned as close to the electrochemical cell window as possible to minimize contributions from the bulk solution. When altering the electrode potential to deposit Pb onto the Ag electrode surface, the electrode was pulled away from the window several mm, the surface allowed to equilibrate at the new conditions, and the electrode repositioned near the cell window for spectral acquisition. 

Figure 14.1 Configuration for spectral acquisition (transmittance, reflectance and transflectance).

It is not usually possible to integrate routine C spectra directly unless specific precautions have been taken. However with proper controls, NMR spectroscopy can be used quantitatively and it is a valuable technique for the analysis of mixtures. To record C NMR spectra where the relative signal intensity can be reliably determined, the spectra must be recorded with techniques to suppress the Nuclear Overhauser Effect and with a long delay between the acquisition of successive spectra to ensure that all of the carbons in the molecule are completely relaxed between spectral acquisitions. 

Taylor, M.)., Spectral Acquisition and Calibration Techniques for the Measurement of Radiative Flux Incident upon Propellant, Propellants, Explosives, Pyrotechnics, Vol. 28, 2003, pp. 18. 

Doty Scientific, Inc. (Columbia, SC, USA) has been relatively successful in incorporating high resolution capabilities into their more standard solid-state MAS probes,32 where, in a traditional application, the extra care may not ever be noticed, but it provides the ability to use one MAS probe for both solid and gel-phase samples. They have introduced a sample insert that permits ready preparation of a number of samples that can be inserted into a MAS rotor for spectral acquisition, then preserved (or discarded) without requiring the dedication of a more expensive rotor. 

N. J. Waters, S. Garrod, R. D. Farrant, J. N. Haselden, S. C. Connor, J. Connelly, J. C. Lindon, E. Holmes and J. K. Nicholson, High-resolution magic angle spinning H-l NMR spectroscopy of intact liver and kidney Optimization of sample preparation procedures and biochemical stability of tissue during spectral acquisition, Anal. Biochem., 2000, 282, 16-23. 

Propene on HY was, therefore, selected for the first in situ variable-temperature study using the CAVERN method. These experiments were carried out in early 1988 and published in 1989 (93). The central features of the CAVERN experiments were that the propene was introduced into the zeolite at cryogenic temperature and the sample was manipulated so that spectral acquisition could commence with an unreacted sample. Additional spectra were then acquired as the sample was slowly raised to room temperature. Detailed experiments of this sort were carried out for propene-2-l3C and propene-7-13C and less extensive experiments were performed for propene-3-13C. These experiments showed, among other things, that the 250 ppm peak was formed coincident with a second peak at ca. 156 ppm and the relative intensities of these peaks were 2 1. A careful study of the literature of carbenium ion chemistry in sulfuric acid and superacid solution media suggested the assignment of these resonances (250 and 156 ppm) to alkyl-substituted cyclopentenyl cations similar to 4. 

Photodiode arrays allow faster spectral acquisition ( l s) than dispersive instruments (which require several minutes). Photodiode array instruments have almost no moving parts, so they are more rugged than dispersive instruments that must rotate the grating and change... 

Fyfe et al. (355) were able to produce a very informative 13C CP/MAS NMR spectrum of the triphenylmethyl carbonium ion by using the tetra-fluoroborate counterion and by employing simultaneous 19F and H decoupling during spectral acquisition (see Fig. 81). The nonequivalence of the ortho and meta carbons is readily seen in the spectrum. 

In FT-IR spectroscopy, a pattern known as an interferogram is obtained in place of the normal spectrum. The interferogram is the Fourier transform of the normal spectrum. Therefore, the normal spectrum can be obtained by transforming the interferogram. The advantages of the FT-IR are simultaneous spectral acquisition and high signal to noise ratio. A detailed description of FT-IR can be found elsewhere [17]. 

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