Reference deconvolution technique

The application of the reference deconvolution technique to overcome the effect of magnetic field inhomogeneity in high-resolution NMR has recently been reviewed by Metz et al.21 In this technique, the observed resonance lineshape from a single resonance line is used to deconvolve the observed lineshapes to produce the Lorentzian lineshapes associated with liquid samples. 

If we consider only a few of the general requirements for the ideal polymer/additive analysis techniques (e.g. no matrix interferences, quantitative), then it is obvious that the choice is much restricted. Elements of the ideal method might include LD and MS, with reference to CRMs. Laser desorption and REMPI-MS are moving closest to direct selective sampling tandem mass spectrometry is supreme in identification. Direct-probe MS may yield accurate masses and concentrations of the components contained in the polymeric material. Selective sample preparation, efficient separation, selective detection, mass spectrometry and chemometric deconvolution techniques are complementary rather than competitive techniques. For elemental analysis, LA-ICP-ToFMS scores high. 

The use of reference deconvolution for the correction of artefacts in nuclear Overhauser effect difference spectroscopy [9] is illustrated by the spectra of fig. 3. The experimental technique used here differs slightly from that normally encountered in using a control spectrum in which the preirradiation is gated off rather than shifted in frequency, and in keeping the decoupler and transmitter at the same frequency. These modifications were... 

Solid-state C NMR spectra of oil shales, obtained by CP/MAS with high-power decoupling are broad because of the multitude of resonances from the different carbon types found in these complex materials. A number of af roaches have been taken to improve the resolution of solid-state NMR of fi il fuels. Such tedmiques include variable temperature studies, variable frequency studies, mathematical enhancements and deconvolution techniques, and relaxation rate methods. The most popular method of enhancing solid-state NMR spectra is a relaxation rate method called dipolar dephasing (DD), which is sometimes referred to as interrupted decoupling. The exploitation of relaxation methods in CP NMR of fossil fuels has been reviewed elsewhere. ... 

Various analytical procedures are applied to extract valence numbers from Lm spectra. They are based on a deconvolution of two superimposed and shifted single-peaked sub-spectra taken either from experimental or from numerical reference spectra. Within Av = +0.1 the different techniques yield the same results on identical spectra. An estimate of the absolute and relative uncertainties may be obtained from table 3. It lists the valence numbers from most of the Lnui spectra published from 1975 until 1986. These numbers have been worked out by more than ten different laboratories. Obviously the numbers extracted from identical systems agree fairly well in spite of the fact that they have been obtained with the use of quite different deconvolution techniques. Large systematic deviations (>0.1) from the average numbers (where available) should be attributed to different experimental results rather than to the specific valence determination procedure. 

One effective way to compensate for many instrumental sources of error is reference deconvolution. Since most instrumental errors (e.g. static field inhomogeneity and magnetic field instability) affect all signals equally, multiplying the experimental FID by the complex ratio of the theoretical and experimental signals for a reference resonance leads to a spectrum in which such errors have been corrected. This technique can be used to ensure that all lines are basically Lorentzian, and also to enforce strict comparability between different spectra in a series, for example to correct noise in multidimensional NMR. 

The major impetus for the development of solid phase synthesis centers around applications in combinatorial chemistry. The notion that new drug leads and catalysts can be discovered in a high tiuoughput fashion has been demonstrated many times over as is evidenced from the number of publications that have arisen (see references at the end of this chapter). A number of )proaches to combinatorial chemistry exist. These include the split-mix method, serial techniques and parallel methods to generate libraries of compounds. The advances in combinatorial chemistry are also accompani by sophisticated methods in deconvolution and identification of compounds from libraries. In a number of cases, innovative hardware and software has been developed tor these purposes. 

Principal component analysis (PCA) [61] was first used to determine the number of independently varying chemical species present and to provide initial estimates of the spectral shapes resulting from these species and of their concentration profiles. Reference ATR FTIR spectra for several components (the solvent acetonitrile and water, the reagent cyclopentyltrichlorosilane and the product o7h3) were measured to assist in the deconvolution of the data. Frequency windows were selected that allowed the best discrimination between the reference compounds (725-775 cm-1 for acetonitrile, 850-900 cm-1 for water and the silsesquioxane). Finally, the MCR technique was applied to the data in the selected frequency windows to find the component spectra and relative concentration profiles that best fit the observed spectra. 

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. 

There are numerous books on digital signal processing (DSP) and Fourier transforms. Unfortunately, many of the chemically based books are fairly technical in nature and oriented towards specific techniques such as NMR however, books written primarily by and for engineers and statisticians are often quite understandable. A recommended reference to DSP contains many of the main principles [29], but there are several similar books available. For nonlinear deconvolution, Jansson s book is well known [30]. Methods for time series analysis are described in more depth in an outstanding and much reprinted book written by Chatfield [31]. 

One method that has been used to acquire carbohydrates is isolation and purification from natural sources such as human or animal tissue, milk, urine, plants, and bacteria (see cross reference Isolation of glycans). Access to homogeneous carbohydrate stmctures can be challenging due to the difficulties in separation of complex mixtures, identification of carbohy-drate(s) contained within each fraction, and preparation of sufficient quantities from the limited amounts present in a particular sample. Alternatively, mixtures of unknown composition can be used to survey a broad repertoire of the glycome. On identification of a mixture containing one or more members with interesting receptor-binding properties, the mixture can then be deconvoluted by further fractionation and separation by routine analytical techniques (13). 

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