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Spectra quantitative applications

Applications of neural networks are becoming more diverse in chemistry [31-40]. Some typical applications include predicting chemical reactivity, acid strength in oxides, protein structure determination, quantitative structure property relationship (QSPR), fluid property relationships, classification of molecular spectra, group contribution, spectroscopy analysis, etc. The results reported in these areas are very encouraging and are demonstrative of the wide spectrum of applications and interest in this area. [Pg.10]

The unique appearance of an infrared spectrum has resulted in the extensive use of infrared spectrometry to characterize such materials as natural products, polymers, detergents, lubricants, fats and resins. It is of particular value to the petroleum and polymer industries, to drug manufacturers and to producers of organic chemicals. Quantitative applications include the quality control of additives in fuel and lubricant blends and to assess the extent of chemical changes in various products due to ageing and use. Non-dispersive infrared analysers are used to monitor gas streams in industrial processes and atmospheric pollution. The instruments are generally portable and robust, consisting only of a radiation source, reference and sample cells and a detector filled with the gas which is to be monitored. [Pg.395]

We choose here instead an analytic formulation based upon the simple molecular lattice, which will immediately be generalized. This will bring the most important concepts to light and provide an interpretation of the spectrum. It can also provide the starting point for a quantitative application of the cluster -Belhc-latticc method use of the Belhc lattice should improve accuracy and reduce the computation required in comparison to the direct cluster technique. [Pg.279]

The cells holding the sample usually display imperfections and are not completely transparent to IR radiation, even when empty. Therefore the base line of the spectrum is rarely set on 100% transmittance and quantitative applications of IR spectroscopy are more complex than for UV-vis (p. 166). [Pg.182]

This time-resolved fluorescence technique allows a measure of the time dependence of fluorescence intensity after a short excitation pulse. It consists of obtaining a spectrum measured within a narrow time window during the decay of the fluorescence of interest. The usefulness of this technique is now well proven for biochemical assays and immunoassays. Lanthanide chelates have luminescence decay times over 600 ps, which allows time-gated fluorecence detection, with a complete rejection of other fluorecence signals. For these quantitative applications, the primary source is generally a quartz lamp associated with a splitter. [Pg.255]

Liquids may be sampled as neat liquids or in solution. A mid-infrared transmission spectrum sufficient for chemical identification may often be recorded from a capillary layer of a nonvolatile, pure liquid. This may be prepared simply from a drop of the liquid that has been sandwiched between a pair of mid-infrared transparent windows clamped together, which is also resistant to attack by the liquid. A more reproducible (and safer) practice, however, is to use an appropriate pathlength cell. Whichever method is selected, the specimen examined must be free from bubbles. For strongly absorbing liquids and some quantitative applications, a more efficient approach may be to use an appropriate infrared internal reflection technique accessory. [Pg.2232]

Solutions Solids may be examined in solution in transmission cells (see the section Liquids ), provided a suitable solvent is available. This can be an effective way of eliminating crystalline lattice effects. ITowever, since no solvent is transparent throughout the entire infrared region, several solvents may be required for complete solute detail, or alternatively an analytically useful difference spectrum may be generated from a single solution, provided solvent-solute interactions are minimal. Solutions offer an important presentation method for quantitative applications, although many of the best solvents are toxic and flammable and must be used with appropriate care, safety, and caution. [Pg.2235]

Quantitative application of Raman spectroscopy generally requires pretreatment to reduce background variance and often also includes the application of chemometric methods. The success of both steps depends on a high level of both abscissa and ordinate stability and linearity. Scattering intensity and the relative intensities of Raman lines within a spectrum depend on a variety of measurement conditions laser power, laser wavelength, spectral resolution, detector properties, and arrangement of the excitation and collection optics. [Pg.265]

Currently, there exists a wide spectrum of applications of NIR-based analysis in the field of polymers. As can be seen from the data in Table 2.9, NIR analysis serves to determine quantitatively terminal double bonds, OH groups, and the content of not only moisture but also of additives such as plasticizers or stabilizers. [Pg.83]

Since natural-abundance peaks in the labelled radicinin were not readily visible in the number of spectral scans employed to make a comparison, the enrichment value of 17% was determined by integration of the C-proton satellite bands of the methyl groups C-11 and C-14, 7i3c-h = 126 Hz, which were evident in the proton 60 MHz spectrum. Combined application with the C-satellite method can thus result in a better quantitative approach to carbon enrichments. [Pg.255]

Equipment technology and processing software for FTIR are very robust and provide a high degree of reliability. Concerns arise for only the most demanding applications. For quantitative work on an isolated feature in the spectrum, the rule of thumb is that the spectrometer resolution be one-tenth the width of the band. FTIR instruments routinely meet that requirement for solids. [Pg.424]

The more advanced spectrofluorimeters are capable of automatically scanning fluorescent spectra between about 200 and 900 nm and produce a chart record of the spectrum obtained. These can also operate at a fixed wavelength and are equally suitable for carrying out quantitative work their main application tends to be for the detection and determination of small concentrations of organic substances. [Pg.734]

The applications of EPR spectroscopy reviewed in the present chapter are based on the sensitivity of the spectrum displayed by iron-sulfur centers to various characteristics, such as the redox state of the center, the distribution of the valences on the iron ions, the nature and the geometry of the ligands, and the presence of nearby paramagnetic species. Although considerable progress has been made during the past few years in the quantitative analysis of these various effects in the case of the conventional iron-sulfur centers described in Section II, the discovery of centers exhibiting unusual EPR properties as... [Pg.484]

The probe molecules of greatest historical interest in catalysis are the Hammett indicators [13]. The difficulty of making reliable visual or spectrophotometric observations of the state of protonation of these species on solids is well known. We have recently carried out the first NMR studies of Hanunett indicators on solid acids [ 14]. This was also the occasion of the first detailed collaboration between the authors of this article, and theoretical methods proved to strongly compliment the NMR experiments. The Hanunett story is told after first reviewing the application of theoretical chemistry to such problems. Central to the application of any physical method in chemistry is the process of modeling the relationship between the observables and molecular structure. However often one does this, it is rarely an exact process. One can rationalize almost any trend in isotropic chemical shift as a function of some variation in molecular structure - after the fact, but the quantitative prediction of such trends in advance defies intuition in most nontrivial cases. Even though the NMR spectrum is a function... [Pg.575]

In this section we focus on methods for the quantitation of a compound in the presence of an unknown interference without the requirement that this interference should be identified first or its spectrum should be estimated. Hyphenated methods are the main application domain. The methods we discuss are generalized rank annihilation method (GRAM) and residual bilinearization (RBL). [Pg.298]

The application of 13C NMR for the rapid analysis of the oil composition of oil seeds is well known [16], 13C NMR has recently been applied to the quantitative analysis of the most abundant fatty acids in olive oil [17]. The values obtained by this method differed by only up to 5% compared with GLC analysis. The quantitative analysis was applied to the olefmic region of the high resolution 13C NMR spectrum of virgin olive oil to detect adulteration by other oils which differed significantly in their fatty acid composition. The application of the methodology for the detection of adulteration of olive oil by hazelnut oil is more challenging as both oils have similar chemical profiles and further experiments are in progress. [Pg.479]

SEC-FTIR yields the average polymer structure as a function of molecular mass, but no information on the distribution of the chemical composition within a certain size fraction. SEC-FTIR is mainly used to provide information on MW, MWD, CCD, and functional groups for different applications and different materials, including polyolefins and polyolefin copolymers [703-705]. Quantitative methods have been developed [704]. Torabi et al. [705] have described a procedure for quantitative evaporative FUR detection for the evaluation of polymer composition across the SEC chromatogram, involving a post-SEC treatment, internal calibration and PLS prediction applied to the second derivative of the absorbance spectrum. [Pg.528]


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See also in sourсe #XX -- [ Pg.583 ]




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