Characterisation of copal resin and amber by negative-ion electrospray ionisation Fourier transform ion cyclotron resonance mass spectrometry.

Copal resin and amber from Columbia were analysed by negative-ion electrospray ionisation (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), with particular focus on polar compounds with relatively high molecular weights. A total of 4038 and 2755 compounds were identified between m/z 150 and 1,000 in the spectra of the copal resin and amber DCM extracts, respectively. The CHO classes were the most abundant species in the detected polar compounds. The petrochemical process of converting copal resin to amber is accompanied by evaporation and dispersion of volatile molecules and polymerisation of relatively smaller molecules. Thus, the most abundant compounds in copal resin comprised more than one C basic unit compared to amber, and the relative abundances of compounds with a high number of carbon and oxygen atoms in amber were higher than those in copal resin. There were strong positive correlations between the double-bond equivalence (DBE ) values and the number of oxygen atoms in both samples. The slopes and y-intercepts of the linear relationship indicated that the C pentadienoic acid is the basic structure of heteroatom compound molecules in copal resin and amber. FT-ICR MS analysis focuses on the characterisation of heteroatom compounds with relatively high molecular weight and is helpful to provide supplementary information on the origin and evolution of complex organic mixtures such as copal resin and amber at the molecular level in a fast and convenient way.