Vibrational spectroscopy overview

T.L. Threlfall and J.M. Chalmers, Vibrational spectroscopy of solid-state forms - introduction, principles and overview, in Applications of Vibrational Spectroscopy in Pharmaceutical Research and Development, D.E. Pivonka, J.M. Chalmers, and RR. Griffiths (Eds), Wiley-Interscience, New York, 2007. 

An overview of basic physics necessary to understand neutron scattering experiments is presented below. This section is a brief introduction to vibrational spectroscopy with neutrons. More details can be found in Ref. [Lovesey 1984], Experienced readers should ignore this rather superficial introduction. 

The chapters fall into major sections covering optical spectroscopy, vibrational spectroscopy, electron paramagnetic resonance, and X-ray spectroscopy. Areas such as nuclear magnetic resonance which have been described extensively in recent volumes of this series have not been included. A general overview of the contents of this volume and examples of problems or situations to which the different approaches have been applied are described in the first chapter. 

Spectroscopic methods can provide fast, non-destructive analytical measurements that can replace conventional analytical methods in many cases. The non-destructive nature of optical measurements makes them very attractive for stability testing. In the future, spectroscopic methods will be increasingly used for pharmaceutical stability analysis. This chapter will focus on quantitative analysis of pharmaceutical products. The second section of the chapter will provide an overview of basic vibrational spectroscopy and modern spectroscopic technology. The third section of this chapter is an introduction to multivariate analysis (MVA) and chemometrics. MVA is essential for the quantitative analysis of NIR and in many cases Raman spectral data. Growth in MVA has been aided by the availability of high quality software and powerful personal computers. Section 11.4 is a review of the qualification of NIR and Raman spectrometers. The criteria for NIR and Raman equipment qualification are described in USP chapters <1119> and < 1120>. The relevant highlights of the new USP chapter on analytical instrument qualification <1058> are also covered. Section 11.5 is a discussion of method validation for quantitative analytical methods based on multivariate statistics. Based on the USP chapter for NIR <1119>, the discussion of method validation for chemometric-based methods is also appropriate for Raman spectroscopy. The criteria for these MVA-based methods are the same as traditional analytical methods accuracy, precision, linearity, specificity, and robustness however, the ways they are described and evaluated can be different. 

For a comprehensive overview of Raman spectroscopy fundamentals, theory, and applications, see (a) McCreery, R. L. in Chemical Analysis Vol 157, Wmefordner J. D, Ed. Wiley New York, 2000. (b) Lewis, I. R. Edwards, H. G. M. Handbook of Raman Spectroscopy, Erom the Research Laboratory to the Process Line Marcel Dekker New York, 2001. (c) Pivonka, D. E. Chalmers, J. M. Griffiths, R R. Eds. Applications of Vibrational Spectroscopy in Pharmaceutical Research and Development WUey New York, 2007. (d) Dollish, F. R. Fateley, W. G. Bentley, F. F. Characteristic Raman Frequencies of Organic Compounds Wiley New York, 1974. 

Several recent overviews of principles and applications of Raman, FTIR, and HREELS spectroscopies are available in the literature [35-37, 124]. The use of all major surface and interface vibrational spectroscopies in adhesion studies has recently been reviewed [38]. Infrared spectroscopy is undoubtedly the most widely applied spectroscopic technique of all methods described in this chapter because so many different forms of the technique have been developed, each with its own specific applicability. Common to all vibrational techniques is the capability to detect functional groups, in contrast to the techniques discussed in Sec. III.A, which detect primarily elements. The techniques discussed here all are based in principle on the same mechanism, namely, when infrared radiation (or low-energy electrons as in HREELS) interacts with a sample, groups of atoms, not single elements, absorb energy at characteristic vibrations (frequencies). These absorptions are mainly used for qualitative identification of functional groups in the sample, but quantitative determinations are possible in many cases. 

This article provides a brief overview of the theory of IR spectroscopy and Raman spectroscopy (for more in-depth descriptions of these methods see Refs. [1-3]). This is followed by a review of vibrational spectroscopic studies performed on clathrate hydrates (a class of inclusion compound) and macrocyclic suprainolecular compounds. Clathrate hydrates were highlighted in this article because of all the clathrate compounds, they are particularly amenable to vibrational spectroscopy and are of great industrial significance. Similar IR/Raman methods can be applied to other well-known clathrate compounds. including quinol and urea " clathrates. Finally, future directions on the use of vibrational spectroscopy in supramolecular compounds will be given. 

Before an examination of the propagation and termination reactions individually, a brief overview of the methods that have been used to obtain profiles of the polymerization rate as a function of time is provided. The photopol5unerization rate can be monitored by any technique that measures a physical quantity which changes as the reaction progresses. In theory, a wide variety of analytical techniques could be used for this purpose (139-148), and new methods are continuously being developed (149). The commonly used methods for obtaining complete polymerization rate profiles are differential scanning calorimetry, fluorescence spectroscopy, and vibrational spectroscopies such as Raman and infrared. 

Infrared (IR) and Raman are both well established as methods of vibrational spectroscopy. Both have been used for decades as tools for the identification and characterization of polymeric materials in fact, the requirement for a method of analysis synthetic polymers was the basis for the original development of analytical infrared instrumentation during World War II. It is assumed that the reader has a general understanding of analytical chemistry, and a basic understanding of the principles of spectroscopy. A general overview of vibrational spectroscopy is provided in Sec. 5 for those unfamiliar with the infrared and Raman techniques. 

In order to provide a minimum basis to put the different vibrational spectroscopies (Raman, MIR, and NIR) into perspective as far as their theoretical and instrumental fundamentals and their individual advantages are concerned, a short comparative overview is given here. For more detailed information the interested reader is referred to the pertinent literature [9-21],... 

This chapter will consider clinical applications which might be met by vibrational spectroscopy, using cancer, infective diseases and vascular surgery as examples and gives a brief overview. This is by no means exhaustive but... 

S. E. Fisher, A. T. Harris, J. M. Chalmers and M. J. Tobin, Head and Neck Cancer a clinical overview and observations from synchrotron-sourced mid-infrared spectroscopy investigations, in Vibrational Spectroscopy for Medical Diagnosis, eds. M. Diem, P.R Griffiths and J. M. Chalmers, John Wiley Sons Ltd., Chichester, 2008, pp. 123-154. 

Interest in the vibrational spectra of adsorbed molecules is at least 40 years old. The past ten years have seen the development of many novel techniques for determining the vibrational spectra of adsorbed species and this symposium brings together a state-of-the-art survey of these techniques. In one s ethusiasm for the recent advances made in any subject there is a tendency to forget the parent technique and its steady contribution to our knowledge. In this case, the parent is simple transmission infrared spectroscopy. This paper, therefore, is an attempt to briefly present an overview of some of the developments which have occurred in the application of transmission infrared spectroscopy to surface studies with emphasis upon results generated in the past 10 years. For more detailed information on work published prior to 1967 the reader is referred to three texts which have appeared on this subject (1-3). 

The identification of species adsorbed on surfaces has preoccupied chemists and physicists for many years. Of all the techniques used to determine the structure of molecules, interpretation of the vibrational spectrum probably occupies first place. This is also true for adsorbed molecules, and identification of the vibrational modes of chemisorbed and physisorbed species has contributed greatly to our understanding of both the underlying surface and the adsorbed molecules. The most common method for determining the vibrational modes of a molecule is by direct observation of adsorptions in the infrared region of the spectrum. Surface spectroscopy is no exception and by far the largest number of publications in the literature refer to the infrared spectroscopy of adsorbed molecules. Up to this time, the main approach has been the use of conventional transmission IR and work in this area up to 1967 has been summarized in three books. The first chapter in this volume, by Hair, presents a necessarily brief overview of this work with emphasis upon some of the developments that have occurred since 1967. 

The second chapter ends with two overviews by Stephens Devlin and by Hug on the theoretical and the physical aspects of two vibrational optical activity spectroscopies (VCD and VROA, respectively). In both overviews the emphasis is more on their basic formalism and the gas-phase quantum chemical calculations than on the analysis of solvent effects. For these spectroscopies, in fact, both the formulation of continuum solvation models and their applications to realistic solvated systems are still in their infancy. 

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