Stability of limonene and monitoring of a hydroperoxide in fragranced products

Upon prolonged exposure to air, limonene is prone to oxidation. Hydroperoxides formed upon oxidation are strong skin sensitizers in animal tests and give positive patch tests in human dermatitis patients. However, there is no analytical evidence indicating potential sources from which the public can be exposed to sufficient quantities of limonene hydroperoxide for induction of skin sensitization to occur. It has been proposed that fragranced products might lead to such exposure. Here, we developed analytical methods using mass spectrometry (MS) in combination with gas chromatography (GC)-MS and liquid chromatography (LC)-MS to detect limonene-2-OOH. GC-MS has a low sensitivity, whereas LC-MS was found to be a sensitive method to detect this hydroperoxide. However, selectivity of LC-MS is low in complex fine fragrances owing to limited separation and unspecific ions. We developed an additional method based on selective reduction of limonene-2-OOH to carveol by triphenylphosphine (PPh3). Quantitative carveol formation from the hydroperoxide in the presence of PPh3 could be verified in hydroperoxide-spiked fragrances. These methods were then applied to stability studies. We found a high stability of limonene in eaux de toilette and the PPh3-reduction assay gave no indication of hydroperoxide formation in repeatedly opened, half-empty bottles stored for 9 months. Aged fine fragrances retrieved from consumers contained an average of 1990 µg/g limonene, but only traces of carveol were formed in a minority of the samples in the presence of PPh3. Control samples were spiked with trans-limonene-2-OOH. Quantitative trans-carveol formation in the presence of PPh3 indicated that the method would detect the hydroperoxide in these consumer products if it was present at higher concentrations. In conclusion, limonene-2-OOH may be detected in complex fragrance samples by selective reduction followed by GC-MS. However, we could not find evidence for significant limonene-2-OOH formation in aged fine fragrance samples