Coupling with FTIR Spectroscopy

Frequently, when analyzing a complex polymer, the first step must be the determination of the gross composition. Only when the chemical structures of the polymer components are known, can sophisticated separation techniques, such as gradient HPLC or LC-CC, be adapted to a specific analysis. 

The most frequently used techniques for a flash analysis are infrared spectroscopy and SEC. Infrared spectroscopy provides information on the chemical substructures present in the sample, while SEC gives a first indication of the molar mass range. Information on both molar mass and composition is obtained 

A rather broad applicability of FTIR as a detector in liquid chromatography can be achieved when the mobile phase is removed from the sample prior to detection. In this case the sample fractions are measured in a pure state without interference from solvents. Experimental interfaces to eliminate volatile mobile phases fromHPLC effluents have been tried with some success [133-135] but the breakthrough towards a powerful FTIR detector has only been achieved by Gagel and Biemann, who formed an aerosol from the effluent and sprayed it on a rotating aluminum mirror. The mirror was then deposited in a FTIR spectrometer and spectra were recorded at each position in the reflexion mode [136-138]. 

As a result of the investigation a complete FTIR spectrum for each position on the disc and, hence, for each sample fraction is obtained. This spectrum bears information on the chemical composition of each sample fraction. The set of all spectra can be arranged along the elution time axis and yields a three-dimensional plot in the coordinates elution time-FTIR frequency-absorbance. 

One of the benefits of coupled SEC-FTIR is the ability to identify directly the individual components separated by chromatography A typical SEC separation of a polymer blend is shown in Fig. 28 [ 142]. Two separate elution peaks 1 and 2 were obtained, indicating that the blend contained at least two components of significantly different molar masses. A quantification of the components with respect to concentration and molar mass, however, cannot be carried out as long as the chemical structure of the components is unknown. 

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The combination of pyrolysis with GC/FTIR was presented by Davies et al. (2002), who showed that gas chromatography coupled with FTIR spectroscopy can be used as a complementary technique to the conventional GC/MS analysis, by an easier determination of structural isomers (e.g.,p-cresol, m-cresols,p-cresol). 

The investigated transients with double bonds to silicon exhibit short effective 1/e lifetimes ranging from a few ms (for H2Si=0) up to ca. 30 ms for 3a. In contrast to these silanes, the kinetic instability of multiply-bonded transient phosphines depends more strongly on the electronegativity of the element involved in the multiple bond to phosphorus. The observed 1/e lifetimes span a substantial range from 8 ms for highly reactive 14a up to stable derivatives with unprotected phosphorus-carbon multiple bonds. FVT coupled with FTIR spectroscopy has proved to be a competitive technique to study robustly bound transients with 1/e lifetimes as short as 8 ms. 

There are many examples of second-order analyzers that are used in analytical chemistry including many hyphenated spectroscopic tools such as FTIR-TGA, IR-microscopy, as well as GC-MS, or even two-dimensional spectroscopic techniques. Another hyphenated technique that is being developed for the study of solid-state transitions in crystalline materials is dynamic vapor sorption coupled with NIR spectroscopy (DVS-NIR).26 DVS is a water sorption balance by which the weight of a sample is carefully monitored during exposure to defined temperature and humidity. It can be used to study the stability of materials, and in this case has been used to induce solid-state transitions in anhydrous theophylline. By interfacing an NIR spectrometer with a fiber-optic probe to the DVS, the transitions of the theophylline can be monitored spectroscopically. The DVS-NIR has proven to be a useful tool in the study of the solid-state transitions of theophylline. It has been used to identify a transition that exists in the conversion of the anhydrous form to the hydrate during the course of water sorption. 

Nature of Adsorbed Species. - The nature of adsorbed species on the catalyst surface has been largely determined by transient reaction studies (with or without isotopes) coupled with surface spectroscopies during transients such as infrared (IR), Fourier transform infrared (FTIR) and NMR. Various catalysts have been studied including Ni, Ru, Rh, Co, and Fe. 

In the field of IR spectroscopy, DR has only recently experienced a wave of renewed interest when coupled with FTIR instrumentation (14-20). There are also recent reports by Hattorl, t al, (21-24) of the design of an emissionless DR-IR grating... 

For process control, analytical techniques such as vibrational spectroscopies, which provide information about paint composition, are important based on (1) the popularization of FT instruments, with a better signal-to-noise ratio and fast data acquisition speed (2) reflectance techniques (total attenuated and diffuse), photoacoustic spectroscopy, and the development of optical fiber-based devices that provide easy spectrometric measurements on crude samples (3) vapor-phase generation coupled with FTIR for fast analysis of the volatile paint fractions ... 

CoupiGd Pyrolysis Techniques. Perhaps the most powerful techniques currently available are those in which the polymer is pyrolyzed for a short time in a pyrolysis system directly coupled to a modem analytical instmment capable of analysis of the volatile products. Although direct pyrolysis coupled with ftir is available, the most common techniques have been gas chromatography, mass spectroscopy, and combinations of the two. In contrast to tga, these techniques provide no real information on the onset temperature of degradation or on the number of distinct stages, but they can give very detailed information about the products of reaction. 

Figure 3 and figure 4 present results of thermogravimetric analysis coupled with Fourier transform infrared speetroscopy (TG-FTIR) and TG coupled with mass spectroscopy (TG-MS). 

The offline (Adrian et al., 2000) and online (Kok, 2004) coupling of FTIR spectroscopy with comprehensive two-dimensional LC (LC x SEC, see Section 7.4.4.) has already been demonstrated. 

This work shows the application of quantitative pyrolysis-gas chromatography coupled with infrared spectroscopy and electron impact mass spectrometry in the study of radiation-induced scission of bisphenol-A polycarbonate (PC). PC under vacuum was gamma-irradiated using a 60Co source in the dose range from 0.125 to 1.0 MGy. This was followed by flash pyrolysis under an inert atmosphere observed by GC-FTIR-MS. Pyrolysis of the irradiated PC gave different products depending on the dose. Yields of carbon dioxide and methane decreased with dose whereas those of phenol and 4-methylphenol increased. The yields of benzene and toluene were unaffected by irradiation. Analysis of the products in this study helped to infer two main pathways for the radiation-induced scission of PC that involve carbonate bond rupture or aliphatic-aromatic bond rupture. 30 refs. 

ANALYSIS OF TECHNICAL POLYMER BLENDS WITH COUPLING OF LIQUID CHROMATOGRAPHY WITH FTIR SPECTROSCOPY... 

The coupling of liquid chromatography with FTIR spectroscopy provides a new and interesting method for the detailed analysis of complex polymer systems. The application of this hyphenated technique to the analysis of polymer blends shows that it is possible to identify the different blend components by their spectral characteristics. Components of different chemical compositions are determined selectively and their chemical structure is analysed through well-resolved FTIR spectra. For structure elucidation, all facilities of... 

Evaporative LC-FTIR is rapidly gaining industrial acceptance as a useful tool in low-MW additive analysis. HPLC has also been coupled with various element-selective detectors. There is significant demand for speciation information for many elements, and the separation ability of chromatography coupled to ICP-MS offers the analyst a versatile tool for such studies. It is apparent that ICP-MS is increasingly being employed for chromatographic detection. Several modes of GC, SFC, LC and CE have been hyphenated with ICP-MS for improved detection limits compared to other traditional methods of detection such as UV-VIS spectroscopy. Inorganic speciation deserves more attention. 

The molecular weight (M , GPO with polystyrene standard) is in the range of 8-14 kD (P 10-30). The M values for the metal-organic polymers are generally lower compared to that of the metal-free organic polymer (Pq). The authors therefore came to the conclusion that the Re-bipyridine monomer 58 is less reactive in the Pd-catalyzed cross-coupling reaction compared to the biphenyl monomer 59. These polymers have also been characterized by and NMR, as well as by FTIR spectroscopy. 

Similarly to FTIR spectroscopy, Raman spectroscopy is a versatile technique of analyzing both organic and inorganic materials that has experienced noticeable growth in the field of art and art conservation, in parallel to the improvement of the instrumentation [38]. In particular, the introduction of fiber optic devices has made feasible the development of mobile Raman equipments, enabling nondestructive in situ analyses [39]. On the other hand, the coupling of Raman spectroscopes with optical microscopes has given rise to Raman microscopy vide infra). 

In the case of an unknown chemical, or where resonance overlap occurs, it may be necessary to call upon the full arsenal of NMR methods. To confirm a heteronuclear coupling, the normal H NMR spectrum is compared with 1H 19F and/or XH 31 P NMR spectra. After this, and, in particular, where a strong background is present, the various 2-D NMR spectra are recorded. Homonuclear chemical shift correlation experiments such as COSY and TOCSY (or some of their variants) provide information on coupled protons, even networks of protons (1), while the inverse detected heteronuclear correlation experiments such as HMQC and HMQC/TOCSY provide similar information but only for protons coupling to heteronuclei, for example, the pairs 1H-31P and - C. Although interpretation of these data provides abundant information on the molecular structure, the results obtained with other analytical or spectrometric techniques must be taken into account as well. The various methods of MS and gas chromatography/Fourier transform infrared (GC/FTIR) spectroscopy supply complementary information to fully resolve or confirm the structure. Unambiguous identification of an unknown chemical requires consistent results from all spectrometric techniques employed. 

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