Fourier-transform infrared spectroscopy sampling techniques

Because of this mathematical step, the technique is usually called Fourier transform infrared spectroscopy or FTIR spectroscopy. The Fourier transformation is a mathematical procedure that enables one to convert from the results of an interfero-gram back to intensities of a given wavelength. It is performed in a computer connected to the spectrometer. The result is the absorption spectrum of the sample, that is, the intensity of the absorbance as a function of the wavenumbers. 

This review covers the theory and application of Fourier transform infrared spectroscopy to the characterization of polymers. The basic theory, the sampling techniques and the spectral operations are described. The applications discussed include the study of polymer reactions, polymer structure and dynamic effects. 

Sampling in surface-enhanced Raman and infrared spectroscopy is intimately linked to the optical enhancement induced by arrays and fractals of hot metal particles, primarily of silver and gold. The key to both techniques is preparation of the metal particles either in a suspension or as architectures on the surface of substrates. We will therefore detail the preparation and self-assembly methods used to obtain films, sols, and arrayed architectures coupled with the methods of adsorbing the species of interest on them to obtain optimal enhancement of the Raman and infrared signatures. Surface-enhanced Raman spectroscopy (SERS) has been more widely used and studied because of the relative ease of the sampling process and the ready availability of lasers in the visible range of the optical spectrum. Surface-enhanced infrared spectroscopy (SEIRA) using attenuated total reflection coupled to Fourier transform infrared spectroscopy, on the other hand, is an attractive alternative to SERS but has yet to be widely applied in analytical chemistry. 

The introduction of Fourier Transform Infrared Spectroscopy (FTIR) brought along a number of typical solid sample techniques. DRIFTS (Diffuse Reflectance Fourier Transform Infrared Spectroscopy) is probably most commonly known. Another technique, developed specifically for measuring solid, opaque samples is PAS (Photo Acoustic Spectroscopy). This accessory is less known, probably due to its high cost and its rather difficult modus operandi. 

Infrared spectroscopy (IR) is one of the oldest instrumental analytical techniques but its value in structural analysis has decreased with the rise of nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS). Compared to the traditional dispersive IR techniques, Fourier transform infrared spectroscopy (FTIR) offers more sampling techniques. 

Gillette PC, Lando JB, Koening JL (1985) A survey of infrared spectral data processing techniques In Ferraro JR, Basile LJ (eds) Fourier transform infrared spectroscopy -applications to chemical systems, Vol 4 Academic Press, New York, 1-47 Graham JA, Grim WM III, Fateley WG (1985) Fourier transform infrared photoacoustic spectroscopy of condensed-phase samples, In Ferraro JR, Basile LJ (eds) Fourier transform infrared) spectroscopy - applications to chemical systems, Vol 4 Academic Press, New York, 345-392... 

Surface analysis is a big challenge for the modihed polymers. It is well known that hydrophilicity and hydrophobicity can be measured in terms of water adhesion tension (x°). x° greater than 30 dyne cm are designated as hydrophilic and x° less than 30 dyne cm are designated as hydrophobic (Ma et al., 2007). Attenuated total reflec-tance-Fourier transformed infrared spectroscopy (ATR-FTIR) and XPS are two widely used techniques for the analysis of surfaces of modihed polymers. ATR-FTIR is not very specihc to the polymer surfaces as the signals are a combination of surfaces and underneath. Therefore, XPS can be used for the surface analysis because this technique has much smaller sampling depth (typically, <10 nm) (Ma et al., 2007). 

Two problems should be considered when conducting an investigation that incorporates mapping and sampling techniques. One problem is that the irreplaceable and fragile nature of the textile evidence demands nondestructive or minimally destructive procedures. Removal of enough microsized samples to provide a statistical sample would destroy much of the textile. Another consideration is that the cost of techniques such as as X-ray diffraction (XRD) or Fourier transform infrared spectroscopy (FTIR) would be prohibitive when applied to a large number of samples. Because of these constraints, chemical and physical data should be obtained from a limited number of locations. These areas can best be identified once a survey of the evidence has been conducted and technical fabrication analyses of evidence obtained from a random sample of locations have been performed. 

Chalmers JM, Mackenzie MW (1988) Solid Sample Techniques. In Mackenzie MW (ed) Advances in Applied Fourier Transform Infrared Spectroscopy. Wiley, Chichester, p 105 Chalmers JM, Willis HA, Cowell GM, Spragg RA (1982) Perkin Elmer Infrared Bulletin 99 Champion JP (1977) Can J Phys 55 1802... 

Fourier-transform infrared spectroscopy (FTIR) is based on the measurement of absorbed light in the infrared range by the sample being analyzed. From the obtained spectra, it is possible to identify specific functional groups and structures. In metabolomics studies, FTIR is used for determination of complex mixtures and can be combined with LC and GC techniques [9, 10]. 

Fourier-transform infrared spectroscopy (FTIR) and pH measurements are the techniques most often adapted for in-line IPC. pH measurements are used for reactions that are run in water or have an aqueous component, e.g., an aqueous extraction. FTIR is especially good for monitoring continuous reactions [12] and reactions that would be dramatically changed by exposure to the atmosphere and temperature of the laboratory. Suitable reactions include low-temperature reactions, reactions run under pressure, reactions with gaseous or toxic materials (e.g., ethylene oxide), and reactions run under inert atmosphere. Further advantages of in-line assays are that no samples need to be prepared, and assay results can be generated within minutes. 

Conclusions from the Case Study. Exercises such as these are quite common in the characterization of complex solids and do indeed require the combined expertise of a group of specialists. The set of techniques required varies from case to case, but the more or less standard combination of two or more complementary techniques as part of the arsenal is very useful. In retrospect, we were able to identify the techniques which were crucial to solving this problem XPS/TEM, LEIS, XRD and EXAFS. A number of others (Magic-Angle-Spinning NMR (MAS-NMR), Raman Spectroscopy and FTIR (Fourier Transform Infrared Spectroscopy) were applied, but did not add significantly to the final result. The study of various samples which were synthesized in different ways and which showed different catalytic activities did prove relevant, but is not described in detail here. 

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