Optimising the analysis of Anacardiaceae (Asian lacquer) polymers using pyrolysis-gas chromatography-mass spectrometry

Abstract

The identification and differentiation of Anacardiaceae or Asian lacquer polymers is a challenging task, however, the characterisation of these lacquers is highly relevant, especially there is a need to understand the degradation of the polymers and the effects of conservation treatments. To improve the characterisation of artificially light aged polymers from Gluta usitata, Toxicodendron succedaneum and Toxicodendron vernicifluum, using pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), the effects of pyrolysis temperature and the use of online derivatisation were studied in detail. Derivatisation was based on trimethylsilylation with hexamethyldisilazane (HMDS) and hydrolysis and methylation with tetramethylammonium hydroxide (TMAH). The results showed that stepwise increasing the flash pyrolysis temperature is helpful to differentiate between primary pyrolysis reactions and the formation of secondary products. This approach was invaluable to reconstruct the polymeric structure of these lacquers, based on the identified pyrolysates, and the peak areas obtained at specific pyrolysis temperature ranges. Derivatisation of polar compounds in the samples proved a requirement to obtain reliable data. Even though the HMDS based results were found to be inferior to the obtained TMAH data, in terms of derivatisation efficiency and overall analytical repeatability, HMDS was more selective towards alkenylcatechols. This appeared primarily for alkenylcatechols comprising the T. succedaneum polymer and for the analysis of carbohydrates, in samples of all polymeric types. Lowering the split flow, showed that the derivatisation efficiency with HMDS was much improved. Using the reduced split flow method also allowed for e.g., better identification of resorcinol isomers in G. usitata polymers.