Fingerprinting techniques spectroscopy

In reality, NMR spectroscopy has broadened the scope and absolute possibility for performing more extensive as well as intensive studies with regard to recording the spectrum of isolated and synthesized organic molecules in addition to their mechanistic and stereochemical details hitherto inaccessible. Therefore, NMR spectroscopy finds its applications for compound identification, by means of a fingerprint technique very much identical to that used in lR-spectroscopy. Besides, it is invariably utilized as a specific method of assay for the individual constituents of a mixture. A few typical examples of drug assays will be dealt separately at the end of this chapter to justify its efficacy and usefulness. 

The detection of a chromophore permits us to deduce the presence of a structural fragment or a structural element in the molecule. The fact that it is the chromophores and not the molecules as a whole that give rise to spectral features is fortunate, otherwise spectroscopy would only permit us to identify known compounds by direct comparison of their spectra with authentic samples. This "fingerprint" technique is often useful for establishing the identity of known compounds, but the direct determination of molecular structure building up from the molecular fragments is far more powerful. 

Konig, I. and Hollatz, R. (1990) A fingerprint technique using Mossbauer spectroscopy for the determination of individual chemical iron species in young sediments. Hypeifine Interact., 57, 2245. 

Infrared (IR) and nuclear magnetic resonance (NMR) are valuable fingerprinting techniques for molecular compounds. They can also give information on new compounds about functional groups present and molecular symmetry. Visible/UV absorption spectroscopy and other techniques are usefiil for investigating electronic structure. 

Together with MS, IR and NMR spectroscopies are the most valuable fingerprinting techniques for molecular compounds. Features of the spectra also enable structural information to be obtained about a new compound, especially the presence of known functional groups and some aspects of its symmetry. 

Mid-infrared (IR) spectroscopy is a well-established technique for the identification and structural analysis of chemical compounds. The peaks in the IR spectrum of a sample represent the excitation of vibrational modes of the molecules in the sample and thus are associated with the various chemical bonds and functional groups present in the molecules. Thus, the IR spectrum of a compound is one of its most characteristic physical properties and can be regarded as its "fingerprint." Infrared spectroscopy is also a powerful tool for quantitative analysis as the amount of infrared energy absorbed by a compound is proportional to its concentration. However, until recently, IR spectroscopy has seen fairly limited application in both the qualitative and the quantitative analysis of food systems, largely owing to experimental limitations. 

In yeasts particularly, chemotaxonomy by means of application of proton magnetic resonance spectroscopy was described by Gofin and Spencer(2), and the acetolysis fingerprinting technique by Kocourek and Ballou(3) can be also used to determine the taxonomy of yeasts. These methods are based on the differences in the chemical structure of their mannan components. Similarly, serological clasification of yeasts by the use of slide agglutinin test was reported by Tsuchiya, Fukazawa and Kawakita(4). 

The search for faster screening methods capable of characterizing propolis samples of different geographic origins and composition has lead to the use of direct insertion mass sp>ectrometric fingerprinting techniques (ESf-MS and EASI-MS), which has proven to be a fast and robust method for propoHs characterization (Sawaya et al., 2011), although this analytical approach can only detect compoimds that ionize under the experimental conditions. Similarly, Fourier transform infrared vibrational spectroscopy (FITR) has also demonstrated to be valuable to chemically characterize complex matrices such as propolis (Wu et al, 2008). 

If a simple qualitative identification of a plastic is all that is required then fingerprinting techniques discussed in Chapter 6 may suffice. Fingerprinting instrumentation discussed include glass transition, pyrolysis techniques, infrared spectroscopy, pyrolysis - Fourier transform infrared spectroscopy, Raman spectroscopy and radio frequency slow discharge mass spectrometry. 

Like other forms of molecular spectroscopy, MS may be used as a fingerprint technique to identify the components of additive systems extracted from polymer compositions. The strengths of MS are high sensitivity and the ability to distinguish between closely related compounds of differing relative molecular mass, e.g., the various alkyl thiodipropionates used as synergistic stabilisers in polyolefins and the UV-absorbing benzotriazole derivatives. 

The direct determination of the structure by means of vibrational spectroscopy is impossible the structure must be known in advance by x-ray, electron, or neutron diffraction methods. Raman spectral analysis, sensu stricto, is based on group theory (see Sec. V.D) applied to isolated molecules or to crystal lattices triply periodic. Raman spectral analysis, sensu lato, includes the identification of the structure of an unknown material as being the same as that of a known material if their Raman spectra are identical this is the fingerprinting technique, which does not require knowledge of which vibration modes are concerned (see Sec. VI). 

High performance spectroscopic methods, like FT-IR and NIR spectrometry and Raman spectroscopy are widely applied to identify non-destructively the specific fingerprint of an extract or check the stability of pure molecules or mixtures by the recognition of different functional groups. Generally, the infrared techniques are more frequently applied in food colorant analysis, as recently reviewed. Mass spectrometry is used as well, either coupled to HPLC for the detection of separated molecules or for the identification of a fingerprint based on fragmentation patterns. ... 

Infrared spectroscopy, which is recognised as an analytical technique with high selectivity and fingerprinting ability for molecular compounds, can be used... 

With recent developments in analytical instrumentation these criteria are being increasingly fulfilled by physicochemical spectroscopic approaches, often referred to as whole-organism fingerprinting methods.910 Such methods involve the concurrent measurement of large numbers of spectral characters that together reflect the overall cell composition. Examples of the most popular methods used in the 20th century include pyrolysis mass spectrometry (PyMS),11,12 Fourier transform-infrared spectrometry (FT-IR), and UV resonance Raman spectroscopy.16,17 The PyMS technique... 

The emerging analytical technique of laser-induced breakdown spectroscopy (LIBS) is a simple atomic emission spectroscopy technique that has the potential for real-time man-portable chemical analysis in the field. Because LIBS is simultaneously sensitive to all elements, a single laser shot can be used to record the broadband emission spectra, which provides a chemical fingerprint of a material. 

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