Direct temperature-programmed pyrolysis

Except for TG, programmable furnaces are rarely interfaced directly to spectroscopic techniques. Davidson [835] has indicated several data processing schemes to extract information about composition and overlapping thermal decomposition reactions of evolved gaseous reaction products of polymers subjected to linear temperature-programmed pyrolysis-infrared spectroscopy. 

Physical and spectral properties of batrachotoxins are presented in Table I. Mass spectra have been presented and interpreted (3,13,14). The parent ion of batrachotoxin is virtually nondetectable by direct probe methods, and instead an apparent molecular ion of miz 399 is seen, probably because of pyrolytic elimination of the pyrrole carboxylate moiety. Batrachotoxin alkaloids do not chromatograph on capillary gas chromatographic columns, but a pyrolysis product has been detected at 280°C on the temperature-programmed, packed OV-1 columns used for analysis of other dendrobatid alkaloids (see Appendix). The pyrrole carboxylate moiety is responsible for major ions of C7H9N02 (m/z 139), C6H9N ... 

Degradative methods based on pyrolysis are the subject of renewed interest due to the identification power offered by gas chromatography-mass spectrometric systems (GC-MS) (Wershaw and Bohner, 1969 Martin et al., 1977 Meuzelaar et al., 1977 Bracewell and Robertson, 1976). There are two main pyrolysis techniques (1) controlling the decomposition kinetics by temperature programming and (2) the use of quasi-instantaneous heating (e.g.. Curie point pyrolysis). The later technique avoids most recombination reactions, but does not allow kinetic control. The pyrolysis effluent can be detected directly (Rock-Eval method) or after chromatographic fractionation. 

Pyrolysis Photoionization GCMS. Details of the instrument have been described earlier (11). Curie point pyrolysis was performed in nitrogen which also served as the carrier gas. Pyrolysis occurred directly in front of the capillary column, which exits in the photoionization chamber of the mass spectrometer. A 50 m fused silica column coated with CP-Sil 5-CB (I.D.=0.32 mm, film thickness 1 micron) was used for the separation. The oven was programmed from 80-260 C after a period at room temperature during pyrolysis of the sample. Argon I resonance photons (11.6 and 11.8 eV) were used for ionization of the GC effluent. Ion source teoqterature was 150°C. Pressure in the ion source was 10 2 Torr and in the vacuum chamber 10" Torr. The quadrupole was scanned at 1 scan/s over 30 to 235 amu. 

In principle, any type of magnetic or quadrupole mass spectrometer can be utilized for the analytical pyrolysis of organic materials, if a direct introduction system capable of producing a desired tempera-ture/time profile is available. For example, direct insertion probes (DIPs) and direct exposure probes (DEPs) are Avidely used for sample introduction and such probes are supplied with control units that allow heating and temperature programming of the sample up to 500-800°C. Therefore, such modules should be considered as the most readily available probes for Py-MS studies. 

Pyrolysis gas chromatography has been used to characterize amine oxides (11). Neutral or slightly acidic pyrolysis conditions give characteristic alkyldimethylamines. Amine oxides may be analyzed by direct injection of the purified materials. At an injector temperature of 220 C, the amine oxide homologs are converted reproducibly to the olefins. These are separated on a column of Apiezon L with a temperature program of 180 to 280 Cat4 C/min(94). 

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