In this blog we come back to the Rt-βDEXsa column and its application to rose oils and fragrance. The Rt-bDEXsa has a significantly different selectivity than the other chiral columns. It provides the best separation of 1-octen-3-ol, carvone, camphor, b-citronellol, and rose oxides, which makes it a good fit for certain essential oils’ analysis. We’ll look at geranium oil, pure rose oil and rose fragrance.
Geranium oil
Geranium is a plant from Rosids clade, thus its oil’s composition is similar to the rose oil. Chiral constituents in geranium oils include cis and trans rose oxides, menthone, linalool, and β-citronellol. The Rt- βDEXsa column provides chiral resolution for all of these compounds. In authentic samples of geranium oil, (-)-(4R)-configured diastereomers of cis– and trans-rose oxides predominate over their (+)-enantiomers. The (-)-(S) form of -citronellol should be 74-80% of the enantiomeric ratio. Note that cis- and trans-rose oxides and β-citronellol are racemic in this particular commercial geranium oil, as shown in Figure 1. These racemic compounds indicate that this oil is not authentic.
Figure 1: Geranium oil on Rt-bDEXsa.
GC_FF1372
Peaks
| Peaks | tR 1 | tR 2 | tR 3 | tR 4 | |
|---|---|---|---|---|---|
| 1. | Rose oxides | 22.701 | 22.931 | 23.370 | 23.616 |
| 2. | (-) Menthone | 28.420 | – | – | – |
| 3. | Linalool (±) | 30.919 | 31.298 | – | – |
| 4. | β-Citronellol (±) | 37.090 | 37.245 | – | – |
| 5. | Geraniol | 39.494 | – | – | – |
Rose oil and rose fragrance
As geranium oil, rose oil also contains rose oxides and β-citronellol (Fig 2). Menthone is present as well, however in a lower amount. In this sample of rose oil, the rose oxides were also in much lower amount than in the geranium and all four isomers were present. The presence of all rose oxides with together with equally abundant β-citronellol enantiomers suggest that this sample is not authentic.
Figure 2: Rose oil on Rt-bDEXsa
GC_FF1373
Peaks
| Peaks | tR 1 | tR 2 | tR 3 | tR 4 | |
|---|---|---|---|---|---|
| 1. | Rose oxides | 22.700 | 22.920 | 23.360 | 23.610 |
| 2. | (-) Menthone | 28.416 | – | – | – |
| 3. | β-Citronellol (±) | 37.066 | 37.230 | – | – |
| 4. | Geraniol | 39.805 | – | – | – |
The rose fragrance had some of the typical components of the rose oil, however, the rose oxides were completely missing (Figure 3).
Figure 3: Rose fragrance on Rt-bDEXsa
This concludes our series on chiral chromatography. If you have any suggestions on expanding the scope, please let us know!
