Spectral subtraction technique

Mrad/h). Films were stored at -20° until analysis could be carried out. Oxidized films and derivatized, oxidized films were characterized by iodometry (reflux with Nal in isopropanol/acetic acid) and by transmission Fourier Transform (FT) IR (Perkin Elmer 1500), using the spectral subtraction technique (3, 14). Free radicals were measured by the electron spin resonance technique (e.s.r., Varian E4 spectrometer). 

Selecting an approach Physical separation of the two compounds will not be easy, but mass spectral subtraction techniques may allow you to obtain a spectrum of the peak of interest. 

Typical features of the spectra of polymers are the changes introduced when the polymer chains are oriented by strain. When observed with polarized radiation the changing orientation of the molecular chains is visible by pleochromism of the infrared bands or the changes of the polarizability in the Raman spectra. Stress relaxation and the effects of fatigue and fracture may be observed, especially when the spectral subtraction technique is applied. These methods are well described by Siesler and Holland-Moritz (1980). In the Atlas of polymer and plastics analysis by Hummel and Scholl (1991) the methods of polymer analysis are described exhaustively and the spectra of plastic material and its constituents are collected. 

Applications of the Spectral Subtraction Technique. Based on the advantage of precision wavenumber measurement provided by computerized FT-IR Instrumentation, the absorbance-subtraction technique has become a practical method in analysis of multicomponent mixtures [ ]. It was also found in this research that difference photoacoustio spectroscopy can be used to distinguish small differences between two samples. By comparing the PAS spectra of treated and untreated materials, the common spectral features can be cancelled out. The remaining bands can be interpreted in terms of the near-surface chemical species due to the treatment. 

Davies. J.E.D. Clathrate and inclusion compounds. Part 8. An investigation of the usefulness of the spectral subtraction technique in analyzing the infrared spectra of clathrates. 

A previous paper [1] reported on the usefulness of the spectral subtraction technique in analysing the infrared spectra of clathrates formed by quinol and by Dianin s compound. Here we report on the use of the technique in analysing the infrared spectra of some intercalates of zirconium phosphate, and the Raman spectra of some clathrates of quinol. 

The spectral subtraction technique can be applied equally successfully in the analysis of both the infrared and Raman spectra of inclusion compounds, revealing guest molecule bands which would otherwise be obscured by the more intense host lattice bands. The spectral addition technique is also shown to be useful in simulating clathrate spectra. 

Patticini [55] has described an IR method for the determination of 1 to 8% of mineral oil in PS. In this method the PS sample is dissolved in carbon tetrachloride, together with known mineral oil standards. The solutions are evaluated by measurements made between 3,100 and 3,000 cm using a spectral subtraction technique. 

Some of the major approaches for noise reduction from speech signals were reviewed. Emphasis of the physical circumstances where each is applicable and the theoretical assumptions upon which each is based were considered. Aural noise reduction systems have been an active area of research for many decades. The theory of Weiner and Kolmologrove was advanced in the 1940s and has been applied for many different speech models since then. However, the utility of the MSE criterion upon which these methods are based has been questioned for speech. In addition, these methods require knowledge of the spectra of speech which, due to the fact that speech is not strictly stationary, are difficult to obtain. Thus approaches, which subscribe a parametric model to the speech signal, have arisen. The MSE criterion has also been applied in the spectral domain to yield the successful spectral subtraction technique. The theoretical justification for... 

Nonnal spontaneous Raman scahering suffers from lack of frequency precision and thus good spectral subtractions are not possible. Another limitation to this technique is that high resolution experiments are often difficult to perfomi [39]. These shortcomings have been circumvented by the development of Fourier transfomi (FT) Raman spectroscopy [40]. FT Raman spectroscopy employs a long wavelength laser to achieve viable interferometry. 

No discussion has been devoted to the recent use of Fourier transform spectrometers rather than dispersion instruments. The ease with which the spectral data can be manipulated and background subtracted make the FT methods particularly useful for studies of surface species, particularly during catalytic reaction. Recently there has been a surge of interest in the coupling of computer subtraction techniques to conventional grating instruments. For many IR surface studies, where only limited frequency range is required, this... 

These techniques are also often referred to as "spectral subtraction . We will not use this terminology in order to avoid ambiguities between the general principle and the particular technique described in [Boll, 1979], nor will we use the term spectral estimation as quite a number of the STSA techniques are not based on a statistical estimation approach. 

A variant on spectral subtraction is the INTEL technique [Weiss et al., 1975], in which the square root of the magnitude spectrum is computed and the rooted spectrum is then further transformed via a second FFT. Processing similar to that described above is then performed in this pseudo-cepstral domain. The estimate of the speech amplitude function in this domain is transformed back to the magnitude spectral domain and squared to remove the effect of rooting the spectrum. 

Subtraction is possibly the most used, and often overused, spectral manipulation technique. It is an extremely useful technique because it attempts to obtain spectra of pure components by removing interfering spectral features caused by solvents or other analytes in mixtures. It is also used to remove unwanted background features. Spectral subtraction can be very successful for separating spectra of pure components in the case of mixtures of solid compounds. As long as the various chemical components do not interact and the S/N ratio is good, subtractions can be very successful. 

The cysteine residues were derivatized to introduce the R1 side chain (Fig. 5A), and the EPR spectra analyzed in terms of R1 mobility (Langen et al., 1999). The EPR spectra each revealed two components reflecting R1 populations of different mobility. Using simulation and subtraction techniques, the two spectral components (a and /3) were resolved and analyzed separately (see Fig. 7B for examples). In each case, the most... 

Steady-state, or dummy, scans are used to allow a sample to come to equilibrium before data collection begins. As in a regular experiment, a number of scans are taken, but data are not collected during what would be the normal acquisition time. Steady-state scans are usually performed before the start of an experiment, but, for certain experiments on older instruments, may be acquired before the start of each incremented time value. This technique is not necessary in typical one-dimensional NMR experiments, but is employed in onedimensional methods that involve spectral subtraction (e.g., DEPT Section 7-2b) and virtually all two-dimensional experiments. 

Infrared (IR) spectroscopy is perhaps the most convenient complementary technique for use with NMR. For example, we show in Fig. 3(a) (61) an IR spectrum of a soluble PHEMA. The polymer contains hydroxyls (3400 cm-1), saturated hydrocarbon functionality (circa 3900 cm-1 and 1500 1300 cm-1), and ester functionality at 1725 cm-1. Deuterium exchange brought about by exposure to d4 methanol vapor may be used to show that the in chain C-C skeletal vibration of PMMA at 1070 cm-1 which has been associated with atactic polymer, (79) has an analogue in PHEMA at 1080 cm-1 (Fig. 3b). Spectral subtraction after deuteration reveals also the primary alcohol C-O stretch of PHEMA at 1025 cm-1. 

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