Qualitative analysis of Copaifera oleoresin using comprehensive two-dimensional gas chromatography and gas chromatography with classical and cold electron ionisation mass spectrometry

摘要

Improved separation of both sesquiterpenes and diterpenic acids in Copaifera multijuga Hayne oleoresin, is demonstrated by using comprehensive two-dimensional gas chromatography (GC x GC) coupled to accurate mass time-of-flight mass spectrometry (accTOFMS). GC x GC separation employs polar phases (including ionic liquid phases) as the first dimension (D-1) column, combined with a lower polarity D-2 phase. Elution temperatures (Te) of diterpenic acids (in methyl ester form, DAME) increased as the D-1 McReynolds' polarity value of the column phase decreased. Since Te of sesquiterpene hydrocarbons decreased with increased polarity, the very polar SLB-IL111 D-1 phase leads to excessive peak broadening in the D-2 apolar phase due to increased second dimension retention ((2)t(R)). 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 (2)t(R). Identities of DAME were aided by both soft (30 eV) electron ionisation (El) 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 El 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 x GC with soft EI accurate mass measurement of terpenes, particularly for unknown phytochemicals. (C) 2016 Elsevier B.V. All rights reserved.