Characterization of Volatile Components of Zingiber roseum Essential Oil Using Capillary GC on Modified Cyclodextrins

Abstract

The essential oil from different parts of Zingiber roseum plants was extracted by hydrodistillation, and analyzed using enantio-GC, capillary-GC and GC-MS. Two chiral selectors, 6-tert-butyldimethylsilyl-2,3-diethyl-beta-cyclodextrin (TBDE-beta-CD), and 2,3,6-methyl-beta-cyclodextrin (PM-beta-CD) doped into 14% cyanopropylphenyl/86% dimethylpolysiloxane, and 35% diphenyl/65% dimethylpolysiloxane, respectively were compared in order to clarify the stereochemistry and enantioselectivity of terpenoids using chiral gas chromatography. The enantiomeric excess for (1R)-(+)-alpha-pinene, (1R)-(+)-beta-pinene, and (R)-(+)-limonene were characteristic for the rhizome. In TBDE-beta-cyclodextrin coated chiral columns, a significant increase in separation factor (alpha) for beta-pinene, limonene, linalool and alpha-terpineol enantiomers was observed when compared with methyl substituted beta-cyclodextrin. The increase in chain length of the alkyl substituents may be the possible cause for enantiomer separation in beta-cyclodextrin cavity. In addition, enantioreversal of alpha-pinene enantiomers in 6-tert-butyldimethylsilyl-2,3-diethyl-beta-cyclodextrin was noticed as a unique feature. The enantiomeric compositions of Z. roseum fruit and flower essential oils were similar, but, in contrast, the rhizome oil contained an entirely different composition. Therefore, these results aid in the authentication of the natural origin of Z. roseum essential oils.