Olibanum, or frankincense, is an oleogum-resin that has been collected since ancient times from barks of Boswellia carterii, B.frereana and other species of Boswellia (Burseraceae), small trees indigenous to northeastern Africa and Arabia [1, 2]. This drug occurs in more or less ovoid tears, 5-25 mm long, which are sometimes stuck together.
The surface is dusty and of a yellowish, bluishwhite or greenish-white tint. Olibanum is used in incense and fumigating preparations [2, 3]. Its powdered form is used in toothache . “White” and “yellow” olibanums are two varieties of African olibanums which are available in Isfahan commercial markets. In order to define the volatile terpenoid composition of the above mentioned olibanums and get more pertinent criteria of identification, we decided to isolate their essential oils and analyze them by gas chromatography and GC-mass spectroscopy (MS) methods.
2. Marerials and methods
2.1. Examined materials
“White” and “yellow” olibanums were obtained from a commercial market in Isfahan (Iran) in 2003. The samples were identified macroscopically and authenticated to be two African olibanums obtained from Boswellia species according to Hairfield et al method .
2.2. Oil preparation
Freshly powdered samples of the “white” and “yellow” olibanums were steam distilled for 4 h. Pale yellow oils (4.0 % and 4.06 %v/w) were obtained which exhibited the following physical properties, respectively: d25: 0.915; h25: 1.4720 and d25: 0.871; h25:1.4770.
2.3. GC analysis
Initially to check the separation of the components, samples were examined by capillary GC using a Perkin Elmer 8500 instrument. The column used was a BP1 capillary column (30 m x 0.25 mm; film thickness: 0.25 µm). The carrier gas was nitrogen with a flow rate of 2 ml/min. The oven temperature was programmed from 60 to 275 °C at 4 °C/min. The injector and detector temperatures were 275 °C and 280°C, respectively.
2.4. GC/MS analysis
Analysis of the volatile constituents was performed on a Hewlett Packard 6890 GC/MS instrument under the following conditions: injection of 0.1 µl samples, HP-5 MS capillary column (30 m x 0.25 mm; film thickness 0.25µm); carrier gas He, flow rate 2 ml/min, the injector temperature 250 oC, temperature program: 60 to 275 oC at 4 oC/min; mass spectra: electronic impact, ionization potential 70 eV, ion source temperature 250 oC, ionization current 1000 µA, resolution 1000, and mass range 30-300.
Identification of the constituents was based on computer matching against the library spectra (Library Database Wiley 275), their retention indices with reference to an nalkane series in a temperature programmed run, interpreting their fragmentation pattern and comparison of the mass spectra with the literature data .
3. Results and discussion
Forty constituents in the oils of the “white” and “yellow” olibanums were identified which accounted for 95.5% and 98.9% of the total oils, respectively (Table 1).
Table 1. Percentage composition of oil constituents of the “white” and “yellow” olibanums available in commercial markets of Isfahan.
*t: trace (less than 0.1%)
The volatile oils of both olibanums are predominantly monoterpenoid in nature (87.7% and 87.3%), with alpha-pinene (34.8% and 48.0%) being the major constituent. However, Verghese et al.  reported that the Indian olibanum oil contains higher proportions of alpha-thujene. Other major monoterpenoids identified in the examined “white” olibanum oil include limonene (15.9%), alpha-thujene (9.0%),
para-cymene (7.0%), myrcene (6.2%) and sabinene (6.0%); while other major monoterpenoids identified in the oil of “yellow” olibanum were limonene (21.7%), myrcene (4.9%) and para-cymene (3.5%).
The predominance of monoterpenoids in the examined samples was in agreement with what was reported by Verghese et al. , Maupetit , and Kasali et al. .
We are grateful to Mrs. Armita Jamshidi for her help in analyzing the oil samples by GC and GC/MS methods.