Recognition of copals in aged resin/ oil paints and varnishes

The polymer fractions of three copals and sandarac were examined with direct temperature-resolved mass spectrometry (DTMS) and pyrolysis - gas chromatography-mass spectrometry (Py-GCMS) with thermally assisted methylation using tetramethylammonium hydroxide (TMAH). They were found to consist mostly of polymers of communic acid and communol. Congo copal contained ozic acid and some enantio-biformene and ozol. A new analytical approach for the identification of polymer fractions in small and insoluble paint samples is introduced. The procedure involves a two-step Py-GCMS technique with on-line derivatisation with TMAH in the first step. In the second step, traces of polymer fractions in small complex samples are analysed. A copal/oil varnish was studied. The characteristic copal components had disappeared to a large extent in the manufacturing process and especially during ageing. However, some characteristic marker compounds could still be found.