Other Analytical Techniques in Pyrolysis

As indicated previously (see Section 1.2) pyrolysis must be associated with an analytical technique in order to provide information on a sample. Several common analytical techniques such as GC, GC/MS or GC/FTIR have been utilized either hyphenated with pyrolysis or off-line and were described previously. Less frequently, techniques such as HPLC, preparative LC, TLC, SFE/SFC, or NMR also have been used for the analysis of pyrolysates. These types of techniques are commonly applied off-line. They are used mainly for obtaining information on that part of the pyrolysate that is difficult to transfer directly to an analytical system such as a GC or for the analysis of materials associated with the char. However, the analysis of the non-volatile part of pyrolysates is frequently neglected, although this leads to an incomplete picture regarding the chemical composition of pyrolysates. 

Besides standard columns, a variety of other column types are known, such as those used for size exclusion, ion exchange, etc. 

Besides thermospray and FAB, other LC/MS ionization techniques are known such as electrospray, or atmospheric pressure ionization (APCI). As LC/MS becomes more common, more studies on pyrolysates using these techniques are likely to be done. 

Another chromatographic technique utilized for the analysis of pyrolysates is thin layer chromatography (TLC) [98, 98a]. TLC can be utilized as an off-line simple technique for the analysis of pyrolysates, with the possibility to visualize the presence of species that do not elute through the stationary phase and remain at the start line of the TLC plate. Supercritical fluid extraction (SFE) and supercritical fluid chromatography (SFC) also have been utilized for the off-line analysis of pyrolysates [99]. The procedure consists of placing off-iine the pyroiysate in the extractor, followed by capillary SFC separation and FID detection of the extract. 

As far as rel. (1) indicates, for one atomic species such as H, or one single precise frequency will be absorbed. However, the nuclei are shielded from an external magnetic field by their electron cloud. The electron density around each nucleus may vary from molecule to molecule [101], and this variation modifies the absorbed frequency as given by rel. (1). The difference in the absorbing frequency of a particular atom from a reference atom is called chemical shift. The result field Ho, which determines the resonance behavior of the nucleus, will be, therefore, different from the applied field Happi, and using a shielding parameter a t can be written  

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