Gas Chromatography-Infrared Spectroscopy Techniques

Infrared spectroscopy can fill some of the current gaps in testing methodology and allow analysts to cope with a wider range of analytical problems (135). Combining MS with infrared (IR) data creates a highly complementary identification system. 

By itself, the entire IR spectrum of an organic compound provides a unique fingerprint, which can be readily differentiated from the absorption patterns of other compounds. This means that when reference spectra are available, most compounds can be unambiguously identified on the basis of their IR spectra. 

These features make IR spectrometry a potentially strong technique for the characterization of chromatographic peaks. However, compared with UV-vis absorbance, extinction coefficients in IR are rather low, and the amount of analyte needed for IR detection therefore is often larger that the amounts usually injected into a GC or LC. Nevertheless, enhanced sensitivity can be achieved by the Fourier transform (FT) version of the infrared spectroscopy (FTIR) (136). 

In the various GC-FTIR systems that are commercially available, three essentially different types of GC-FTIR interfaces can be identified (137). With the most commonly used interface, the GC column effluent flows through a heated light-pipe, and vapor-phase spectra are collected in real time at 1 s intervals. This 

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