SOP: Volatile Oil in Spices (Modified Clevenger Method)
GIFSQ — Global Institute for Food Safety & Quality
Principle
The volatile oil is distilled with water from the spice sample and collected in a graduated Clevenger trap of the design suited to the oil’s density; the volume of oil collected, read to 0.02 ml, gives the volatile oil content as per cent volume by weight.
Apparatus required
- Volatile oil traps, Clevenger type with 29/42 ground glass joints: (a) lighter-than-water design for oils with densities less than that of water, and (b) heavier-than-water design for oils with densities greater than water
- Flask: short neck, round bottom flask of 100 ml to 2 litre capacity depending on the nature of the material and the percentage of volatile oil, with 29/42 ground glass joint to fit the trap and 24/40 joint to take the condenser
- Condenser: West type (tubular), water-cooled drip-tip condenser 40 cm with 24/40 ground glass joint
- Oil bath heated either electrically or by gas flame
- Asbestos wrapping (if considerable splashing occurs in the neck of the trap)
Reagents
a. Xylene: 1 ± 0.01 ml added to the graduated trap for oils whose density is nearly one (e.g., cassia oil); subtract 0.93 ml from the total volume obtained.
b. 10% sodium chloride solution (used instead of water in the flask for cassia oil).
c. Saturated sodium chloride solution: a few ml added to the trap if separation of oil and water is not satisfactory.
d. Anhydrous sodium sulphate (minimum amount, for drying oil required for further examination).
e. Glass beads and silicone antifoam reagent (one or two drops).
Procedure
Clean the apparatus, particularly the trap and the condenser, with cleaning mixture, and rinse with distilled water to prevent sticking of water droplets and facilitate separation of oil globules
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Weigh accurately a sample sufficient to yield 2 to 5 ml of oil, and transfer to the flask using water to aid quantitative transfer
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Fill the flask to about half the capacity with water (with 10% sodium chloride solution instead of water for cassia oil) and mix by swirling; add glass beads and one or two drops of silicone antifoam reagent
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Select the proper Clevenger trap and fill it with water (add 1 ± 0.01 ml of xylene to the graduated trap before connecting the condenser when the density of the volatile oil is nearly one, as in cassia oil)
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Set up the apparatus so that the condensate will not drop directly on the surface of the liquid in the trap but will run down the side
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Heat the flask with stirring, and maintain a distillation rate of 1 to 1.5 drops per second
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If considerable splashing occurs in the neck of the trap, wrap that part with asbestos
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Continue distillation until two consecutive readings taken at intervals of 1 hr show no change in the volume of oil in the trap
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Cool to room temperature, allow to stand until the oil layer is clear, and read the volume of the oil collected to the nearest 0.02 ml
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If the separation of oil and water is not satisfactory, agitate the liquid in the trap with a wire inserted through the condenser; if this fails, carefully add a few ml of a saturated sodium chloride solution to the trap
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To determine the volume of the oil distilled, subtract 0.93 ml from the total volume obtained when xylene was added
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If the oil is required for further examination, drain the oil, dry with the minimum amount of anhydrous sodium sulphate, and store in a glass-stoppered container in a refrigerator
Calculation
Volatile oil % (v/w) = (Volume of oil (ml) × 100) / Weight of sample (g)
Where,
- Volume of oil (ml) = volume of oil collected in the trap, minus 0.93 ml where xylene was added
- Weight of sample (g) = weight of the spice sample taken
Precautions
- Do not heat the flask by a direct flame, on account of the danger of charring the material containing volatile oil — use the oil bath.
References
Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.
- Official Methods of Analysis, Association of Official Analytical Chemists, 12th edn., 30.020, p. 555 (1975).
- Official Analytical Methods, American Spice Trade Association, 2nd edn., Method 5.0, p. 8 (1968).