Fingerprint technique Raman spectroscopy

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. ... 

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... 

Raman spectroscopy is very useful in identifying vibration modes (phonons) in solids. This means that structural changes induced by external factors (such as pressure, temperature, magnetic fields, etc.) can be explored by Raman spectroscopy. It is also a very useful technique in chemistry, as it can be used to identify molecules and radicals. On many occasions, the Raman spectrum can be considered to be like a fingerprint of a substance. 

Since IR spectroscopy is a standard, and perhaps currently the most widely used tool in the search for and characterization of polymorphs, there are likely to be thousands of references to the use of the technique in connection with polymorphs. The vast majority of these deal with the determination of the IR fingerprint of a polymorphic modification. In this section, we wish to note a few cases in which the IR and Raman techniques were employed to obtain chemical information somewhat beyond the mere identification of a particular crystal modification. For instance, Mathieu (1973) showed for a number of chiral compounds that it is possible to distinguish between a dl racemate and a conglomerate of d and / crystals by use of IR and/or Raman spectroscopy, even when it may not be possible to make such a distinction by physical or visual means. 

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. 

In mid-infrared spectroscopy, Fourier transform instruments are used almost exclusively. However, in Raman spectroscopy both conventional dispersive and Fourier transform techniques have their applications, the choice being governed by several factors [133], [134]. Consequently, a modern Raman laboratory is equipped with both Fourier transform and CCD-based dispersive instruments. For a routine fingerprint analysis, the FT system is generally used, because it requires less operator skill and is quicker to set up the FT system is also be tried first if samples are highly fluorescent or light sensitive. However, if the utmost sensitivity is required, or if Raman lines with a shift smaller than 100 cm" are to be recorded, conventional spectrometers are usually preferred. 

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). 

Extending this novel use for the technique, it is possible to use Raman imaging techniques to obtain Raman data from particles deposited from fingerprints at crime scenes to determine if illicit drugs were present on a suspect, and using surface-enhanced Raman spectroscopy, very low levels of detection (around 0.2 fjLg/mm ) could be achieved for narcotics [22]. 

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