Scope and limitations of several pyrolysis methods in the structural elucidation of a macromolecular plant constituent in the leaf cuticle of Agave americana L

Cuticles of Agave americana contain a substantial amount of an insoluble, non-hydrolyzable macromolecular substance of a highly aliphatic nature. Based on Fourier transform infrared (FTIR) and 13 C cross-polarization magic angle spinning NMR spectroscopy it was established that the isolated macromolecular substance consists of a polysaccharide and polymethylene moiety in an estimated ratio of 60:40 by weight. After treatment with acid this ratio changed to 37: 63. The isolates obtained before and after the acid treatment were subjected to Curie-point pyrolysis-gas chromatography with flame ionization detection, Curie-point pyrolysis-gas chromatography/mass spectrometry, Off-line pyrolysis in combination with gas chromatography and gas chromatography/mass spectrometry, desorption chemical ionisation mass spectrometry, time/temperature-resolved pyrolysis-field ionization mass spectrometry and heating experiments in a closed system in order to elucidate the molecular structure. Each of the methods applied has its own specifications with respect to pyrolysis conditions and response factors of different classes of pyrolysis products. The data obtained are highly complementary and, in combination with FTIR and 13 C NMR, several new features of the insoluble, non-hydrolyzable aliphatic biopolymer were revealed.