GC/FTIR coupling

Table 7.25 Main characteristics of GC-FTIR coupling Advantages...

A relatively new and modern analytical method in flavour analysis is the GC-FTIR-coupling technique. This method together with GC-MS-coupling represents the most sophisticated and flexible analytical technique with respect to the quality and the quantity of information. 

New developments in analysis utilizing GC-MS have included GC-FTIR coupled with high-resolution El and CI-MS to identify drinking water contaminants and GC-IR-MS to examine contaminated water, clay, and soil samples. GC-MS, LC-nuclear magnetic resonance (NMR), and LC-MS have been used to identify contaminants in industrial landfill leacheate. Online systems have also been developed such as the measurement of organic contaminants in water samples. MIMS has allowed the development of commercial in situ devices that are now on the market (see above). Almost all combinations of preconcentration, separation, and mass detection have seen significant advances. 

For the analysis of complex mixtures, modern coupling techniques such as GC-MS, GC-FTIR, HPLC-MS, CE-MS and comprehensive two-dimensional GC [832, 836-838a] are valuable and sometimes essential tools. 

G. Full, G. Krammer and P. Schreier, On-line coupled HPLC-HRGC A powerful tool for vapor phase FTIR analysis (LC-GC-FTIR) , J. High Resolut. Chromatogr. 14 160-163 (1991). 

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). 

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. 

Principal component analysis is most easily explained by showing its application on a familiar type of data. In this chapter we show the application of PCA to chromatographic-spectroscopic data. These data sets are the kind produced by so-called hyphenated methods such as gas chromatography (GC) or high-performance liquid chromatography (HPLC) coupled to a multivariate detector such as a mass spectrometer (MS), Fourier transform infrared spectrometer (FTIR), or UV/visible spectrometer. Examples of some common hyphenated methods include GC-MS, GC-FTIR, HPLC-UV/Vis, and HLPC-MS. In all these types of data sets, a response in one dimension (e.g., chromatographic separation) modulates the response of a detector (e.g., a spectrum) in a second dimension. 

Gas Chromatography-Fourier Transform Infrared Spectroscopy - Coupling (GC-FTIR)... 

GC-Fourier transform infra-red (GC-FTIR) spectroscopy is less frequently used than GC-MS, but involves a similar principle in which the outlet from the column is coupled to an infra-red spectrophotometer. The technique currently suffers from a lack of library spectra, as the IR spectra taken in the vapour phase can be subtly different from condensed-phase spectra or spectra collected using the well-established KBr disc method. 

Coupled techniques such as GC/FTIR and HPTC/FTIR require that chromatograms are displayed in real time on the screen. Consequently, the mobile phase exiting the column is sampled at very short time intervals throughout the elution. IR spectra must be calculated rapidly. They serve to construct a pseudochromatograms called Gram-Schmidt according to the mathematicians whose method is used to treat the data. The individual IR spectra are obtained in differed time (Figure 10.21). 

GC is often coupled with the selective techniques of spectroscopy and electrochemistry to provide powerful tools for separating and identifying the components of complex mixtures, Combinations of GC with mass spectrometry (GC /MS), Fourier transform infrared spectroscopy (GC/FTIR), nuclear magnetic resonance spectroscopy, and electroanalytical methods arc sometimes termed hyphenated methods. 

Improvements in analytical capability for the analysis of complex pyrolysate mixtures have appeared during the last decade high-resolution capillary GC with more polar and selective stationary phases coated on inert fused-silica colmnns coupling of capillary GC with sensitive, selective, and lower-cost mass spectrometric detectors enhanced pyrolysis-MS techniques hyphenated analysis methods, including GC-Fourier-transform infrared spectroscopy (GC/FTIR) and tandem MS and better strategies for handling complex multidimensional pyrolysis data. The present chapter reviews the known chemotaxonomy of miCTOorganisms, summarizes practical considerations for the use of pyrolysis in microbial characterization, and critically discusses selected applications of analytical pyrolysis to microbial characterization. 

GC-MS has already been mentioned as the premier method for qualitative analysis (see Chapter 10). A complementary identification technique is Fourier Transform infrared coupled to gas chromatography (GC-FTIR). 

Since IR is nondestructive, it is possible to couple both the IR and the MS to the same gas chromatograph, producing GC-FTIR-MS. The special requirements and some applications have been described [8,14],... 

The combination of gas chromatography (GC) with Fourier transform infrared spectroscopy (FTIR) has gradually become the important analytical tool for qualitative and quantitative analysis of complex mixtures. Numerous applications have been reported in previous reviews. Separation and identification of components in complex mixtures can be a daunting task. GC is the most common technique for separation of volatile and semivolatile mixtures. It is well accepted that when GC is coupled with spectral detection methods, such as MS, NMR, or FTIR spectrometry, the resulting combination is a powerful tool for the analysis of complex mixtures. 

---