Identification System, Spectroscopic

Even in modern quality control laboratories you will find a number of traditional methods for the identification of single flavour compounds, for example the estimation of optical rotation, refractive index, density and melting point, since these methods are generally accepted, effective and less time-consuming. Especially for the purpose of fast identification checks of more complex systems, spectroscopic methods, above all infrared (IR) and near-IR spectroscopy, are gaining more and more importance. 

Pharmaceuticals and drugs] ruggedness test, 848-864 system suitability test, 865 ralidation data elements specific to TLC, 848 mobile phase selection, 822 quality assurance of experimental data and documentation, 865-867 role of TLC in drug analysis, 868-873 chromatqgrapliic identification. 871 spectroscopic identification, 871-873 role of TLC in pharmaceutical analysis, 867-868 sensitivity to experimental conditions 821-822 stationary phase selection, 822 types of analytical aims in pharmaceutical analysis, 823... 

Plastics identification by spectroscopic techniques has increasingly focused on the use of near-infrared and Raman spectroscopic techniques. LLA Instruments, in conjunction with Daimler-Chrysler [78] have developed a superfast near-infrared (NIR) sensor system that has been used to separate mixed plastics by type from shredded automotive parts. NIR spectroscopy uses the near infrared region of the electromagnetic spectrum (from about 800 to 2500 nm). Their two-phase process initially separates bright and colored polymers and black polypropylene from the mix. A second long-wavelength NIR sensor is employed to then separate black plastics such as PC, PMMA, ABS, PC/ABS blends, and others. 

An added difficulty that arises in the in-situ spectroscopic study of electrocatalytic systems in solution is that the active species will be located in the vicinity of the electrode so that the material in solution will generally represent a large background signal making the detection and identification of related species difficult. Thus, it would be ideal to be able to probe only that region proximal to the electrode surface and furthermore to be able to obtain structural information of the species involved. 

B.R. Wood, P. Heraud, S. Stojkovic, D. Morrison, J. BeardaU and D. McNaughton, A portable Raman acoustic levitation spectroscopic system for the identification and environmental monitoring of algal cells. Anal. Chem., 77, 4955-4961 (2005). 

Infrared (IR) spectroscopy was the first modern spectroscopic method which became available to chemists for use in the identification of the structure of organic compounds. Not only is IR spectroscopy useful in determining which functional groups are present in a molecule, but also with more careful analysis of the spectrum, additional structural details can be obtained. For example, it is possible to determine whether an alkene is cis or trans. With the advent of nuclear magnetic resonance (NMR) spectroscopy, IR spectroscopy became used to a lesser extent in structural identification. This is because NMR spectra typically are more easily interpreted than are IR spectra. However, there was a renewed interest in IR spectroscopy in the late 1970s for the identification of highly unstable molecules. Concurrent with this renewed interest were advances in computational chemistry which allowed, for the first time, the actual computation of IR spectra of a molecular system with reasonable accuracy. This chapter describes how the confluence of a new experimental technique with that of improved computational methods led to a major advance in the structural identification of highly unstable molecules and reactive intermediates. 

Another technique which is very helpful in the identification of various systems using spectroscopic properties is the determination of the experimental polarizations of the observed transitions. This also greatly simplifies the overall interpretation of IR spectra of organic systems, particularly in the case of latter molecules. By obtaining these experimental polarizations one is able to break down a complicated spectrum into its symmetry groups and compare them each individually with the calculated frequencies and intensities of the corresponding symmetries. 

The experienced catalytic chemist or chemical reaction engineer will immediately recognize that the study of a new catalytic reaction system using an in situ spectroscopy, has a great deal in common with the concepts of inverse problems and system identification. First, there is a physical system which cannot be physically disassembled, and the researcher seeks to identify a model for the chemistry involved. The inverse in situ spectroscopic problem can be denoted by Eq. (2). Secondly, the physical system evolves in time and spectroscopic measurements as a function of time are a must. There are realistic limitations to the spectroscopic measurements performed. For this reason as well as for various other reasons, the inverse problem is ill-posed (see Section 4.3.6). Third, signal processing will be needed to filter and correct the raw data, and to obtain a model of the system. The ability to have the individual pure component spectra of the species present in... 

The quality of the system identification results is strongly dependent on the manner in which the spectroscopic measurements are made. In this regard, the time-scale of the individual spectral measurements Tgpect is crucial. Many good resolution FTIR, Raman, UV-VIS, fluorescence and H, F,"P NMR spectra can be obtained in 100 s or less. Also, many VCD, ECD, and 2D NMR spectra can be obtained in 1000 s or less. 

Most of the spectroscopic investigations discussed above were carried out on well-defined metallocene systems, either isolated species or those generated from a well-defined metallocene alkyl precursor activated with one equivalent of a borane or borate activator. Most practical polymerisation catalysts, on the other hand, include a scavenger, usually an aluminum alkyl, and may contain ill-defined activators such as methylaluminoxane (MAO), usually at high MAO/Zr ratios. Such systems are less amenable to quantitative studies nevertheless, the identifications of species such as those depicted in Schemes 8.5-8.8 has enabled similar compounds to be identified in more complex mixtures. An idea of the possible mode of action... 

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