Vibrational spectroscopy instrumentation

J.P. Coates, Vibrational Spectroscopy Instrumentation for Infrared and Raman Spectroscopy , Appl. Spectrosc. Rev., 33(4), 267 25 (1998). 

Coates, J. 1997. "Vibrational Spectroscopy Instrumentation for Infrared and Raman Spectroscopy." In G. Ewing, ed. Analytical Instrumentation Handbook (2nd ed.) (pp. 393—555). New York Dekker. 

More specialized techniques are often useful in form characterization. For example, TG-infrared spectroscopy or TG-mass spectroscopy combinations allow identification of volatile materials, making hydrate or solvate identification easier. Variable-temperature and variable-humidity sample chambers on XRPD or vibrational spectroscopy instruments provide the ability to watch crystal form changes associated with changing conditions. The decision to use such methods depends on the characteristics of the particular drug substance under study. 

In the remaining body of this chapter, a description of the ISLS experiment is provided along with a description of our high-pressure vibrational spectroscopy instrumentation. Subsequent to the experimental descriptions, theoretical formalisms are presented. 

Figure 5.2 Laborato vibrational spectroscopy Instrument modified for production use. Courtesy Dow Chemical.

J Coates. Vibrational spectroscopy Instrumentation for infrared and Raman spectroscopy. Appl Spectrosc Rev 33 267-425, 1998. (Reprinted from Analytical Instrumentation Handbook, New York Marcel Dekker, 1997.)... 

Vibrational Spectroscopy. Infrared absorption spectra may be obtained using convention IR or FTIR instrumentation the catalyst may be present as a compressed disk, allowing transmission spectroscopy. If the surface area is high, there can be enough chemisorbed species for their spectra to be recorded. This approach is widely used to follow actual catalyzed reactions see, for example. Refs. 26 (metal oxide catalysts) and 27 (zeolitic catalysts). Diffuse reflectance infrared reflection spectroscopy (DRIFT S) may be used on films [e.g.. Ref. 28—Si02 films on Mo(llO)]. Laser Raman spectroscopy (e.g.. Refs. 29, 30) and infrared emission spectroscopy may give greater detail [31]. 

The development of methods and instrumentation, especially in the high field range, will already open up quite new areas of uses already in the near future. These may at least partly replace and complete solid-state vibration spectroscopy in the polymer field in cases where the amount of material is not the limiting factor. As far as we are able to predict the future, the development of exact quantitative methods of analysis, in particular, will rapidly develop to a high degree of accuracy. 

The importance of the degree of esterification (%DE) to the gelation properties of pectins makes it desirable to obtain a fast and robust method to determine (predict) the %DE in pectin powders. Vibrational spectroscopy is a good candidate for the development of such fast methods as spectrometers and quantitative software algorithms (chemometric methods) becomes more reliable and sophisticated. Present poster is a preliminary report on the quantitative performance of different instrumentations, spectral regions, sampling techniques and software algorithms developed within the area of chemometrics. 

Le Bourdon, G., Adar, F., Moreau, M. et al. (2003) In situ characterization by Raman and IR vibrational spectroscopies on a single instrument deNO, reaction over a Pd/y-Al203 catalyst, Phys. Chem. Chem. Phys., 5, 4441. 

Vibrational spectroscopy is based on the interaction between light and matter it probes the different vibrational states of the investigated molecules. A number of excellent books describing the principles, instrumentation and applications are available [7,8]. 

Vibrational spectroscopy measures and evaluates the characteristic energy transitions between vibrational or vibrational-rotational states of molecules and crystals. The measurements provide information about nature, amount and interactions of the molecules present in the probed substances. Different methods and measurement principles have been developed to record this vibrational information, amongst which IR and Raman spectroscopy are the most prominent. The following focuses on these two techniques, the corresponding instrumentation and selected applications. 

As this chapter aims at explaining the basics, operational principles, advantages and pitfalls of vibrational spectroscopic sensors, some topics have been simplified or omitted altogether, especially when involving abstract theoretical or complex mathematical models. The same applies to methods having no direct impact on sensor applications. For a deeper introduction into theory, instrumentation and related experimental methods, comprehensive surveys can be found in any good textbook on vibrational spectroscopy or instrumental analytical chemistry1"4. 

Clearly, the potential applications for vibrational spectroscopy techniques in the pharmaceutical sciences are broad, particularly with the advent of Fourier transform instrumentation at competitive prices. Numerous sampling accessories are currently available for IR and Raman analysis of virtually any type of sample. In addition, new sampling devices are rapidly being developed for at-line and on-line applications. In conjunction with the numerous other physical analytical techniques presented within this volume, the physical characterization of a pharmaceutical solid is not complete without vibrational analysis. 

Having seen the number of papers devoted to bioprocess analyses utilizing vibrational spectroscopy, it cannot be considered an experimental tool any longer. Manufacturers are responding to pressure to make their instruments smaller, faster, explosion-proof, lighter, less expensive, and, in many cases, wireless. Processes may be followed in-line, at-line, or near-line by a variety of instruments, ranging from inexpensive filter-based to robust FT instruments. Raman, IR, and NIR are no longer just subjects of feasibility studies they are ready to be used in full-scale production. 

Implementing this level of automation intelligence has been the most difficult to realize within manufacturing industries. That is, while automation controls integration of simple univariate instruments (e.g., a hlter photometer) is seamless, it is much more problematic for multivariate or spectral instruments. This is due to the tower of babble problem with various process spectroscopic instraments across process instrument manufactures. That is, the communications protocols, wavelength units and hie formats are far from standardized across spectral instruments, even within a particular class of techniques such as vibrational spectroscopy. Several information technology (IT) and automation companies have recently attempted to develop commercialized solutions to address this complex problem, but the effectiveness of these solutions has yet to be determined and reported. 

Vibrational spectroscopy, in the form of mid-IR, NIR and Raman spectroscopy has been featured extensively in industrial analyses, both quality control (QC), process monitoring applications and held-portable applications [1-6]. The latter has been aided by the need for advanced instrumentation for homeland security and related HazMat applications. Next to chromatography, it is the most widely purchased classihcation of instrumentation for these measurements and analyses. Spectroscopic methods in general are favored because they are relatively straightforward to apply and to implement, are rapid in terms of providing results, and are often more economical in terms of service, support and maintenance. Furthermore, a single spectrometer or spectral analyzer, in a near-line application, may serve many functions, whereas chromatographs (gas and liquid) tend to be dedicated to only a few methods at best. 

A wide variety of instrumental techniques, including X-ray diffraction, thermal analysis, electron microscopy, MAS-NMR and infrared spectroscopy, have been employed at different levels of complexity to investigate the effects of mechanochemical treatment on kaolin. Unfortunately, vibrational spectroscopy has only been used at a superficial level in the study of milled kaolin despite the considerable contribution that it has made to the understanding of the structure and reactivity of kaolin itself. 

Stark, E.W., Near-Infrared Array Spectrometers. In Chalmers, J.M. and Griffiths, P.R. (eds), Handbook of Vibrational Spectroscopy, vol 1 John Wiley 8c Sons New York, 2002, pp. 393-422. Goldman, D.S., Near-Infrared Spectroscopy in Process Analysis. In Meyers, R.A. (ed.), Encyclopedia of Analytical Chemistry, vol 9 Process Instrumental Methods John Wiley 8c Sons New York, 2000, pp. 8256-8263. 

Raman and infrared vibrations are mutually exclusive and consequently use of both techniques is required in order to obtain a set of vibrational bands for a molecule. The advent of powerful computer-controlled instrumentation has greatly enhanced the sensitivity of these vibrational spectroscopies by the use of Fourier transform (FT) techniques, whereby spectra are recorded at all frequencies simultaneously in the time domain and then Fourier transformed to give conventional plots of absorbance versus frequency. The wide range of applications of FT Raman spectroscopy is discussed by Almond et al. (1990). Specific examples of its use in metal speciation are the observation of the Co-C stretch at 500 cm-1 in methylcobalamin and the shift to lower frequency of the corrin vibrations when cyanide is replaced by the heavier adenosyl in going from cyanocobalamin to adenosylcobalamin (Nie et al., 1990). 

Applications of laser-based vibrational spectroscopy to explosive detection have been widely studied. The literature on this topic was summarized by Steinfeld and Wormhoudt [1] and by Henderson [2] in 1998. Instrumentation for explosive detection was summarized by Moore [3] in 2004. 

This article presents the application of a novel technique, which combines the structural sensitivity of vibrational spectroscopy with the conformational sensitivity of chiroptical methods to study the solution conformation of biological molecules. Instrumental aspects, computational methods and spectral results for peptides and nucleic... 

Vibrational spectroscopy is a very versatile and, chemically, well-resolved technique for the characterization of carbon-oxygen functional groups. The immense absorption problems of earlier experiments seems to be overcome in present times with modem FT-IR, DRIFTS or photoacoustic detection instruments. 

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