SOP: Solubility of Essential Oils in Alcohol
GIFSQ — Global Institute for Food Safety & Quality
Principle
Successive volumes of alcohol of defined concentration are added to the oil until a clear solution first appears; the mixture is then diluted further and watched for opalescence or cloudiness, and the behaviour is reported as the number of volumes of alcohol of stated concentration that produce each change in appearance.
Apparatus required
- 10 ml glass-stoppered graduated cylinder
Reagents
a. Alcohol solutions, prepared by mixing 95% alcohol and distilled water in the following proportions by weight, with the strength checked and adjusted if necessary:
| Concentration of alcohol required (% by volume) | 95% alcohol (by volume) | Distilled water |
|---|---|---|
| 50 | 460 | 540 |
| 60 | 564 | 436 |
| 70 | 676 | 324 |
| 80 | 796 | 204 |
| 90 | 927 | 73 |
| 95 | 1000 | 0 |
b. Standard opalescence solution: mix 0.2 N sodium chloride and 0.5 ml of 0.1 N silver nitrate solution as follows to get opalescent solutions of different degree — note the book’s body text reads “0.02 N solution of sodium chloride” while its table header reads “0.2 N NaCl”; the 0.2 N form is used here as given in the table:
| Degree of opalescence | 0.2 N NaCl (ml) | Volume made up with water (ml) | 0.1 N AgNO₃ (ml) |
|---|---|---|---|
| Faint | 0.25 | 50 | 0.5 |
| Slight | 0.50 | 50 | 0.5 |
| Distinct | 1.00 | 50 | 0.5 |
c. Standard turbidity solution: using 0.1 N H₂SO₄ and approximately 1.0 N barium chloride solution, prepare solutions of different degrees of turbidity as follows:
| Degree of turbidity | 0.1 N H₂SO₄ (ml) | Volume made up with water (ml) | 0.1 N BaCl₂ (ml) |
|---|---|---|---|
| Faint | 0.25 | 50 | 0.2 |
| Slight | 0.50 | 50 | 0.2 |
| Distinct | 1.00 | 50 | 0.2 |
Procedure
Pipette 1.0 ml of the oil into a 10 ml glass-stoppered graduated cylinder, and add slowly in small proportions the alcohol of the specified concentration
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Shake the contents thoroughly after each addition
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When a clear solution is first noticed, record the number of volumes of alcohol added
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Continue addition of alcohol up to the 10 ml mark; if opalescence or cloudiness occurs during the subsequent additions of alcohol, note the point at which the phenomenon occurs
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If a clear solution is not obtained at any point during the addition of alcohol of a particular concentration, repeat the procedure using alcohol of the next higher concentration
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Report the behaviour of the material, specifying the volume and the concentrations of the alcohol used corresponding to the changes in the appearance of the mixture
Clear, opalescent and turbid solutions are identified as follows:
- Clear: a clear and bright solution.
- Opalescent: compared with the standard opalescence solutions (faint, slight, distinct).
- Turbid: compared with the standard turbidity solutions (faint, slight, distinct).
References
Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.
Methods of Sampling and Test for Natural and Synthetic Perfumery Materials (First Revision), IS: 326—1968, ISI, New Delhi.