Spectroscopic imaging techniques Raman spectroscopy

Infrared and Raman spectroscopy provide complementary images of molecular vibrations, because in these spectroscopic techniques the mechanisms of the interaction of light quanta with molecules are quite different. 

Infrared spectroscopy performed both in the mid-IR [70] and near-IR [71] provides the potential of rapid determination with little or no sample preparation. Raman spectroscopy also has demonstrated capability for pharmaceutical analysis [72], Vibrational spectroscopic techniques are effective for compositional and structural characterization, as well as quantitation. However, bulk spectrosocpy is ineffective for measuring the spatial distribution and architecture of actives, which are heterogeneously distributed within intact tablets. Raman chemical imaging equipped with multivariate image processing capabilities is a powerful approach to the analysis of pharmaceutical tablet architecture. 

Although a combination of spectroscopy imaging e.g. /xXRF, /xFTIR, /xRS) would offer a powerful way to characterise materials various hurdles must be overcome to achieve the ultimate in integrated spectroscopic imaging. These difficulties include spatial resolution, specimen preparation, spectroscopic probe penetration depth and image integration. Same-spot (optical, /u-FTIR, /u.RS) technology is now available. The topic of Raman microscopy in combination with other microanalysis techniques (electron microscopy/X-ray microanalysis ion mi-croprobe mass spectrometry, and laser microprobe mass spectrometry), i.e. dual-use microprobe systems, has been discussed [534]. 

At first, an overview of the experimental methods which are suitable to characterize the CNT aggregation state in general, and thus are suitable to monitor CNT debundling in aqueous medium and in presence of surfactant, will be reviewed. Three main streams will be presented (i) "direct imaging of the CNT dispersions by m icroscopic techniques (ii] spectroscopic techniques, such as Raman spectroscopy, which exploit the difference in electronic properties between bundled and individualized CNTs and (iii] depolarized dynamic light scattering which is commonly used to characterize colloidal systems. 

Therefore, during the past 30 years, numerous vibrational spectroscopic methods (near infrared, NIR infrared, IR and Raman spectroscopy) have been introduced as very efficient alternatives, which are widely used today to determine fats, proteins, and carbohydrates and also numerous secondary plant substances occurring in agricultural products. For authentication purposes, the mentioned spectroscopic techniques can provide the valuable data in a few minutes, allowing the discrimination of different agrofood samples. Also new developments of IR and Raman microscopes have considerably extended the field of application. These sophisticated techniques allow to perform point-by-point measurements (mapping) or to acquire simultaneously spectra (imaging) from a small sample area. 

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