Wintergreen and Birchwood essential oils contain more than 98% methyl salicylate. As high priced essential oils, they are prone to adulteration by synthetic methyl salicylate derived from phenol (a fossil fuel-based precursor). Any addition of synthetic methyl salicylate to wintergreen or birch wood oil would not change the percentages of minor components significantly. So the monitoring of minor components fails in the case of wintergreen or birch wood essential oil adulteration. Chiral ratios of pure essential oil components is another way to authenticate any essential oil containing chiral molecules, but methyl salicylate is a non-chiral molecule, and a chiral GCMS is not going to work in this case.
Synthetic methyl salicylate is derived from the petrochemical-based precursor phenol, so C14 testing could be the best way for detecting adulteration like this. APRC has observed several times C14 testing has limitations on identifying synthetic methyl salicylate as well. Accuracy percentages vary between 3-5% in detecting synthetic methyl salicylate by C14 testing.
APRC has realized that the synthetic marker-based technique is more reliable than other techniques for some adulteration. In a synthetic process of methyl salicylate from phenol, it produces a trace byproduct called Dimethyl 2-hydroxyterephthalate, which is a synthetic marker of methyl salicylate. If any lab knows how to detect those markers properly, they will be able to see such tiny synthetic markers, even upon the addition of less than 1% synthetic methyl salicylate in any wintergreen or birchwood essential oils.
Watch the synthetic route and mechanism of marker formation in synthetic methyl salicylate at https://youtu.be/za79Kaf9Szo