Spectral manipulation techniques

Spectral Manipulation Techniques. Many sophisticated software packages are now available for the manipulation of digitized spectra with both dedicated spectrometer minicomputers, as well as larger main - frame machines. Application of various mathematical techniques to FT-IR spectra is usually driven by the large widths of many bands of interest. Fourier self - deconvolution of bands, sometimes referred to as "resolution enhancement", has been found to be a valuable aid in the determination of peak location, at the expense of exact peak shape, in FT-IR spectra. This technique involves the application of a suitable apodization weighting function to the cosine Fourier transform of an absorption spectrum, and then recomputing the "deconvolved" spectrum, in which the widths of the individual bands are now narrowed to an extent which depends on the nature of the apodization function applied. Such manipulation does not truly change the "resolution" of the spectrum, which is a consequence of instrumental parameters, but can provide improved visual presentations of the spectra for study. 

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 real power of the CDP s Phase Vocoder package is the great number of tools available for spectral manipulation techniques (Wishart, 1994). There are currently over 60 tools in the package for tasks such as ... 

In summary, it has been shown that deconvolution can be used to pull apart overlapped features and help in the interpretation of mixture spectra. However, remember the limitatious of this technique and the precautions that must be followed to use it properly. On the whole, deconvolution is a useful spectral manipulation technique when used with proper precautions. 

Equation 9 represents the IR spectmm (intensity versus wavenumber), which can be derived from expression (8) using a mathematical technique known as Fourier transformation. Needless to say, this requires spectrometer-interfaced computing power, which additionally provides the capacity for spectral manipulation such as deconvolution, smoothing, and subtraction. 

The range of IR bands that can be utilized to assess hydration alludes to the pervasiveness of water absorbance in an IR spectrum Water is a strong IR absorber and thus can pose a particular difficulty in the spectral examination of aqueous samples. The advent of computer-interfaced FT systems allowing spectral manipulation (such as band subtraction) can circumvent these difficulties, as can the use of specialized accessories such as ATR elements [3] and even alternative vibrational spectroscopic techniques, e.g., FT-Raman spectroscopy. FT-Raman spectroscopy, providing complementary information to IR, has in recent years been employed for the characterization of human SC [185-190] and model SC lipids [191], as well as for the noninvasive monitoring of topically applied compounds [192] and the in vitro evaluation of SC-enhancer interactions [193]. 

T vo approaches can be adopted for dealing with the overlap problem. Firstly, simple sample preparation such as centrifugal ultrafiltration can be used to remove the macromolecules. This results in a spectrum of all the nonprotein-bound metabolites contributing to the spectrum. Alternatively, to avoid s unple manipulation, a spectral editing technique can be applied. It has... 

Many sophisticated data manipulation techniques used in NMR spectroscopy were ushered in together with Fourier transform NMR. Specifically, FT introduced spectroscopists to the power of dealing with information in both the time and frequency domains. These data manipulation techniques are also available for use on cw spectra, which can be Fourier transformed into the time domain to carry out such operations, if necessary, and then transformed back to the spectral representation. Having the opportunity to manipulate the data both in the time and the frequency domain adds greatly to the ability to refine the data. 

Both instrument design and capabilities of fluorescence spectroscopy have greatly advanced over the last several decades. Advancements include solid-state excitation sources, integration of fiber optic technology, highly sensitive multichannel detectors, rapid-scan monochromators, sensitive spectral correction techniques, and improved data manipulation software (Christian et al., 1981 Lochmuller and Saavedra, 1986 Cabaniss and Shuman, 1987 Lakowicz, 2006 Hudson et al., 2(X)7). The cumulative effect of these improvements have pushed the limits and expanded the application of fluorescence techniques to numerous scientific research fields. One of the more powerful advancements is the ability to obtain in situ fluorescence measurements of natural waters (Moore, 1994). 

A set of experiments on gas-liquid motion in a vertical column has been carried out to study its d3mamical behavior. Fluctuations volume fraction of the fluid were indirectly measured as time series. Similar techniques that previous section were used to study the system. Time-delay coordinates were used to reconstruct the underl3ung attractor. The characterization of such attractor was carried out via Lyapunov exponents, Poincare map and spectral analysis. The d3mamical behavior of gas-liquid bubbling flow was interpreted in terms of the interactions between bubbles. An important difference between this study case and former is that gas-liquid column is controlled in open-loop by manipulating the superficial velocity. The gas-liquid has been traditionally studied in the chaos (turbulence) context [24]. 

Chemical separation techniques can be used to reduce spectral interferences and concentrate the analyte. These techniques include solvent extraction(39) and hydride generation(39, 46, 47). At Imperial College, the hydride generation technique is being used on a daily basis(46) for the analysis of soils, sediments, waters, herbage, and animal tissue. The solvent extraction technique is ideally suited for automated systems where the increased manipulation is carried out automatically, and a labor intensive step and sources of contamination are avoided. 

ESR Spectroscopy. Electron Spin Resonance spectroscopy is an important technique for investigating the role of radical intermediates in radiation chemistry. The technique has been used widely for many years in the study of radicals occurring in irradiated solid polymers (.6,7). However, by their very nature, such species are reactive and may only exist in low concentration. The identification of these species can also be a problem since in the majority of polymers the environment of the radicals leads to broad, unresolved ESR spectra, which makes detailed spectral analysis difficult. In recent years, many of these problems of sensitivity and resolution have been reduced by more sensitive and stable ESR spectrometers and by development of new methods of data handling and manipulation. 

The data manipulating capability of a computerized infrared spectrometer allows the spectroscopist to delve more deeply into the structural origin of the infrared absorptions by using data processing techniques to purify, manipulate, and correlate the spectra. If one can systematically vary the relative amounts of various structural contributions, absorbance subtraction can be used to isolate the spectral contributions of the structural components. 

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... 

Finally, for routine applications, our software provides a database management system called BASIS for storage and manipulation of chemical information. BASIS can access generally available spectral libraries from three different spectroscopic techniques (MS, H-NMR and F13C-NMR, IR), and permits the creation of new libraries. For structure elucidation and substructure search of unknown compounds, library search algorithms allow the retrieval of identical and structurally similar spectra. 

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