Exploiting the versatility of vacuum-assisted headspace solid-phase microextraction in combination with the selectivity of ionic liquid-based GC stationary phases to discriminate Boswellia spp. resins through their volatile and semivolatile fractions.

Abstract

The frankincense resins, secreted from Boswellia species, are an uncommon example of a natural raw material where every class of terpenoids is present in similar proportions. Diterpenoids (serratol, incensole, and incensole acetate) are used to discriminate samples from different species and origins. Headspace solid-phase microextraction has been used for frankincense analysis, although it requires long sampling time for medium- to low-volatility markers; headspace solid-phase microextraction under vacuum can overcome this limit. Gas chromatography is used for analysis but the separation of incensole and serratol needs polar stationary phases. In this study, we develop a method to discriminate frankincenses based on vacuum-assisted headspace solid-phase microextraction combined with fast gas chromatography-mass spectrometry with ionic liquid-based stationary phases. The optimized conditions for solid samples were: air evacuation below 0°C, 15min of incubation time, and 15min of extraction time. Losses of volatiles due to vial air-evacuation in the presence of the sample were minimized by sample amount above 100mg and low sample temperature. Fast gas chromatography provides the baseline separation of all markers in 20min. By applying vacuum sampling and fast gas chromatography, the total analysis was reduced to 50min compared to 120min (60min sampling plus 60min analysis) as previously reported. The method was successfully applied to commercial frankincense samples.