Beneath the Peel: Characterizing Citrus Aromas with GC-TOFMS

Both lemons and limes have strong citrus odors, but the difference between these fruits is wide at an analyte level. Identifying these differences is not as easy as it first seems, but the Pegasus® BT and the automated data processing software included in its ChromaTOF® brand software make finding the peaks easy.

Lemon and Lime Chromatographs
TIC Chromatogram for lemon and lime essential oils. Some key analytes with citrus odor types are highlighted.

A quick glance at a representative GC-MS chromatogram for lemon and lime essential oils shows obvious similarities and differences. Both citrus oils are high in limonene, a compound with strong citrus odor characteristics. E-citral, on the other hand, is clearly resolved at a much higher level in lemon essential oil than in lime. This is another citrus-odor compound, but it displays as an obvious difference between the two samples.

What is immediately obvious to the naked eye on the chromatograms, however, does not tell the full story. For example, there is a peak in the lime essential oil that is much lower in the lemon essential oil, indicating a compound that is much more present in the lime sample. The automated peak finding ability of the ChromaTOF brand software, however, was able to determine that this peak was actually caused by the coelution of two distinct analytes. One of the analytes, identified as tetrahydro-2,2-dimethyl-5-(1-methyl-1-propenyl)-furan, was actually only in the lime essential oil sample, with citrus odor properties that included spicy, minty, and woody notes. The presence of this analyte was obscured completely by the presence of trans-ß-ocimene, which has herbal odor properties.

Chromatographic Peak Indexes for Lemons and Limes
What appeared to be one analyte at higher levels in lime compared to lemon, was deconvoluted to two distinct analytes.
One is higher in lime than lemon (m/z 93.10) and the other was only observed in lime (m/z 139.16)

The powerful deconvoluting software, combined with the sensitive, full-mass-spectra scan of the Pegasus BT, enabled these differences to be brought to light, so we could see what you might have otherwise been missing. For a more detailed look at how the citrus profile of lemon and lime essential oils was characterized, read the app note.