Chemical differentiation of Boswellia sacra and Boswellia carterii essential oils by gas chromatography and chiral gas chromatography–mass spectrometry

► Differentiation of Boswellia sacra and Boswellia carterii frankincense species. ► Chiral GC–MS of monoterpenes. ► Optical rotation of frankincense essential oils. ► Enantiomeric ratios of chiral compounds. Major botanical and scientific references currently identify two species of frankincense, Boswellia carterii and Boswellia sacra, as being synonymous. We evaluated the Somalian (B. carterii) and Omani/Yemeni (B. sacra) species by chemical analyses to determine if there were any minor or major differences between the two species of frankincense. Components identified with their average percent for B. sacra are α-thujene (0.6%), α-pinene (68.2%), camphene (2.1%), sabinene (2.9%), β-pinene (2.0%), myrcene (0.7%), limonene+β-phellandrene (6.2%). Components identified with their average percent for B. carterii are α-thujene (7.9%), α-pinene (37.3%), camphene (0.8%), sabinene (4.9%), β-pinene (1.8%), myrcene (7.3%), limonene+β-phellandrene (14.4%). Initially, GC–MS analysis did not reveal major statistical differences. However, optical rotation values, B. Sacra (+30.1°) and B. carterii (−13.3°), demonstrated a greater significant difference. Enantiomeric ratio (+)/(−) values of α-pinene for B. sacra and B. carterii are 8.24 and 0.68, respectively, were also calculated aiding our conclusion that B. sacra and B. carterii are not synonymous but rather two distinct and individual frankincense species.