Spectroscopy and Microspectroscopy

Next to PLM, IR spectroscopy (principally, micro-IR) makes up the most important family of techniques in fiber analysis. As with PLM, IR spectroscopy is minimally destructive or nondestruchve and is useful on even the smallest fiber fragments. Microspectrophotometry (MSP) probes the chemical identification of the synthetic fiber, colorants, and other treatments. MSP is indispensable in the comparative analysis of questioned and known fibers, the central task of most forensic fiber analysis cases. The caveat is that such comparisons require knowledge of typical inter- and intrasample variation. Consider, for example, a pair of blue jeans typically, fibers from along the seams and hems are worn compared with fibers to other portions of the garment. Also, the source from which a sample is obtained will clearly affect any visible spectra and color analysis. Along a single fiber, characteristics of a dye or colorant will vary as well. Such inherent variations must be factored into any conclusions drawn from a comparative analysis, be it of dye or chemical composition. 

The three types of MSP used in fiber analysis are visible (and, to a lesser extent, UV), FTIR, and, increasingly, Raman. Fluorescence techniques sometimes also play a role. 

UV/VIS The topic of colorants and color analysis was introduced in the previous chapter textiles represent one of the most important forensic applications of colorant chemistry and analysis. Colorant analysis and comparison and the use of chromaticity coordinates were discussed in detail in the previous chapter all are applicable to fibers. The plotting of CIELAB coordinates is useful in comparing colors and shades. Some fibers are metameiic, meaning that their color will appear different under different Uluminants. Textiles are often designed to have this property. Metameric fibers perceived as being the same color are distinguished by different UV/VIS spectra. 

The interesting and challenging aspect of colorant analysis in fibers is often the size of the exhibit, which may be as little as a lone fragment of a single fiber. It is a simple task to obtain a UV/VIS spectrum on a swatch of fabric with an 

Major Minor Angle to axis length axis length X-axis 

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FTIR imaging suffers from low signal to noise compared to other types of FTIR spectroscopy and microspectroscopy [106,107]. However, the major sources of error in an imaging system arise from detector noise and not from optical components of the imaging system (for example, apertures). The major factors in this regard are ... 

To summarize, at present an ideal IR source to be used for IR spectroscopy and microspectroscopy is a low emittance, stable low energy storage ring with the highest possible current, possibly working in top-up mode, to perform the most demanding research that is not possible with conventional sources. 

Written by an international panel of experts, this volume begins with a comparison of nonlinear optical spectroscopy and x-ray crystallography. The text examines the use of multiphoton fluorescence to study chemical phenomena in the skin, the use of nonlinear optics to enhance traditional optical spectroscopy, and the multimodal approach, which incorporates several spectroscopic techniques in one instrument. Later chapters explore Raman microscopy, third-harmonic generation microscopy, and nonlinear Raman microspectroscopy. The text explores the promise of beam shaping and the use of a broadband laser pulse generated through continuum generation and an optical pulse shaper. 

Also the infrared microspectroscopy (IR) is a vibrational spectroscopy, but it presents some differences with respect to Raman spectroscopy and also provides different information. In infrared spectroscopy the sample is radiated with infrared light, whereas in Raman spectroscopy a monochromatic visible or near infrared light is used. In this way, the vibrational energy... 

Fig. 8.1 Raman microspectroscopy as combination of surface-enhanced Raman spectroscopy and confocal microscopy...

As to combinatorial chemistry, internal reflection spectroscopy is especially suited for the analysis of the surface of solid polymer substrates, known as pins or crowns (5). With FTIR accessories like the SplitPea (6-8) or the Golden Gate (9), which combine internal reflection and microspectroscopy, direct observation of the chemical synthesis on pins is possible (10). This is shown in Fig. 2 where the spectra of a Mega Crown with linker, Fmoc1-protected (upper curve), and of the same crown after the removal of the pro-... 

NMR has become a standard tool for structure determination and, in particular, for these of Strychnos alkaloids. The last general article in this field was authored by J. Sapi and G. Massiot in 1994 [65] and described the advances in spectroscopic methods applied to these molecules. More recently, strychnine (1) has even been used to illustrate newly introduced experiments [66]. We comment, here, on their advantages and sum up the principles of usual 2D experiments in Fig. (1) and Fig. (2) (COSY Correlation SpectroscopY, TOCSY TOtal Correlation SpectroscopY, NOESY Nuclear Overhauser Enhancement SpectroscopY, ROESY Rotating frame Overhauser Enhancement SpectroscopY, HMQC Heteronuclear Multiple Quantum Coherrence, HMBC Heteronuclear Multiple Bond Correlation). This section updates two areas of research in the field new H and 13C NMR experiments with gradient selection or/and selective pulses, 15N NMR, and microspectroscopy. To take these data into account, another section comments on the structure elucidation of new compounds isolated from Strychnos. It covers the literature from 1994 to early 2000. 

Many polymeric samples are often available in small quantities for analysis. For example, new synthetic polymers are usually available in small quantities and forensic specimens may be limited in availability. In many situations, the identification and/or quantification of such samples are critical. However, samples smaller than the diameter of the probing beam lead to spectral artifacts, which complicate identification and quantification. Hence, many of these microsamples cannot be appropriately analyzed by conventional wide beam spectroscopy in their native state and microspectroscopy presents perhaps the only route to obtain artifact free spectra and consequently, the best chance of material identification. 

Undoubtedly the most powerful method of study in academic laboratories has been ir spectroscopy, advanced rapidly in recent years by the development of FTIR and microspectroscopy and by rapid improvement in sampling methods. Infrared spectroscopy can easily detect the formation of hydroxyl and carbonyl species, and a common technique is to monitor the time dependence of the so-called carbonyl index, the ratio of the intensity of the carbonyl absorption envelope to that of a chosen reference band. 

The methodology of Raman spectroscopy is rapidly becoming matured. Here, we describe two classes of new Raman spectroscopies, Raman microspectroscopy and low-frequency Raman spectroscopy, that are considered to be important for future applications to ionic liquid studies. 

Infrared microspectroscopy has been reviewed [436,444 47] and theory and applications have been described in several recent books [393,417-419], An introduction to step-scan FTIR is available [448]. The role of IR and Raman microscopy/ microprobe spectroscopic techniques in the characterisation of polymers, their products, and composites was reviewed [449]. McClure [450] has described NIR imaging spectroscopy and a recent review on time-resolved studies of polymers by mid-and near-infrared spectroscopy has appeared [451]. Near-infrared microspectroscopy and its applications have been reviewed [452]. 

On-line/in-line technology for monitoring extrusion processes, including FTIR microscopy, near-IR spectroscopy and optical microscopy was reviewed [500]. Several reviews describe uFTIR applications to polymers [458,501]. Line map applications of /U.FTIR have been discussed [491]. A recent review [502] refers to a large number of FTIR mi-crospectroscopic studies as an important source of structural and spatial information for polymer-based articles. A monograph describes applications of FTIR microspectroscopy to polymers [393]. ASTM E 334 (1990) describes the general techniques of infrared microanalysis. 

Time-resolved optical spectroscopies in vitro, x-ray crj taUography, and microspectroscopies in vivo can provide thorough information on the kind and the time-scale of primary molecular reactions occurring in the photoreceptor unit, up to some tiny detail of molecular rearrangements following the absorption of the photon. ... 

XANES spectroscopy is also the basis of chemically sensitive X-ray imaging, as well as qualitative and quantitative microspectroscopy [306], ptXANES is attractive for chemical analysis, with its spatial resolution down to 10 ptm. Variations on the theme are surface EXAFS (SEXAFS), grazing incidence XAS and in situ time-resolved XAS investigations. Grazing angle XAFS can be used for the study of ultrathin multilayer systems. 

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