In order to improve pyrolysis chromatographic analysis of materials that release polar functional groups e.g. carboxylic acids, a simple and rapid methylation method based on TDU-pyrolysis/ GC-MS in the presence of tetramethylammonium hydroxide (TMAH) was developed. Linseed oil was selected as test material because of its high triglyceride content comprising both saturated and unsaturated fatty acids. Pyrolysis was performed at 500, 600 and 700 °C using a GERSTEL pyrolysis module (PYRO) with a heated platinum filament. The optimum pyrolysis temperature for linseed oil was found to be 500 °C. The fatty acids in the linseed oil were found to have been quantitatively methylated when using a methanolic TMAH solution (~ 10 % in methanol). The use of an aqueous TMAH solution (25 wt. % in H2O) for the methylation of fatty acids was found to result in lower fatty acid methyl ester (FAME) yields, indicating that the formation of a homogeneous mixture of sample and reagent is essential. Additionally, it was evident that the reagent plays an active role in cleaving the triglycerides. Automated direct injection of the reagent into the TDU-PYRO is possible, but this function is a special adaptation. Chromatograms obtained from direct injection of 1 μL TMAH solution into the linseed oil sample show no difference compared with those obtained after manually mixing linseed oil and the TMAH solution prior to pyrolysis.
The pyrolysis- and thermochemolysis-GC-MS methods were successfully used to determine the molecular composition of Eocene amber from the Ameki formation, Nigeria. The amber was pyrolyzed at 480 °C for 20 s with and without adding TMAH. Free carboxylic acids were quantitatively methylated to their corresponding methyl ester products in the presence of TMAH. Both Pyrolysis-GC-MS and thermochemolysis-GC-MS chromatograms were used to determine the structural class and botanical source of the fossilized resin. The pyrolysis products were dominated by labdane type diterpenoids and some sesquiterpenoids, which point to a conifer (gymnosperm) botanical source of the resin.