Improved separation of both sesquiterpenes and diterpenic acids in Copaifera multijuga Hayne oleoresin, is demonstrated by using comprehensive two-dimensional gas chromatography (GC × GC) coupled to accurate mass time-of-flight mass spectrometry (accTOFMS). GC × GC separation employs polar phases (including ionic liquid phases) as the first dimension (1D) column, combined with a lower polarity 2D phase. Elution temperatures (Te) of diterpenic acids (in methyl ester form, DAME) increased as the 1D McReynolds’ polarity value of the column phase decreased. Since Te of sesquiterpene hydrocarbons decreased with increased polarity, the very polar SLB-IL111 1D phase leads to excessive peak broadening in the 2D apolar phase due to increased second dimension retention (2tR). The combination of SLB-IL59 with a nonpolar column phase was selected, providing reasonable separation and low Te for sesquiterpenes and DAME, compared to other tested column sets, without excessive 2tR. Identities of DAME were aided by both soft (30 eV) electron ionisation (EI) accurate mass TOFMS analysis and supersonic molecular beam ionisation (cold EI) TOFMS, both which providing less fragmentation and increased relative abundance of molecular ions. The inter-relation between EI energies, emission current, signal-to-noise and mass error for the accurate mass measurement of DAME are reported. These approaches can be used as a basis for conducting of GC × GC with soft EI accurate mass measurement of terpenes, particularly for unknown phytochemicals.
- Accurate mass measurement
- Cold electron ionisation
- Copaifera multijuga
- Diterpenic acid methyl esters
- Ionic liquid column