SOP: Residue After Steam Distillation

GIFSQ — Global Institute for Food Safety & Quality

Principle

The oil is steam-distilled until 100 ml of water collects; the non-volatile residue is recovered from the distillation flask and from the distillation products by chloroform and ether extraction, dried and weighed, giving the residue as a percentage of the sample.

Apparatus required

• Steam distillation assembly as shown in the book’s Fig. 11.4
• 250 ml distillation flask
• 125–250 ml separating funnel
• Tared 150 ml beaker
• Boiling water bath

Reagents

a. Dilute HCl (1 + 2): one or two drops, if there is a tendency for emulsification.

b. Alcohol.

c. Chloroform.

d. Ether.

Procedure

In the distillation flask of 250 ml capacity, take 50 ml of water, and pipette 15 ml of oil

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Pipette another 15 ml of oil to a weighing bottle and note the weight

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Connect the flask to the apparatus, heat the contents to boiling point, and let the steam in; adjust the flame such that the water level in the flask remains approximately constant

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Adjust the rate of distillation to approximately 200 ml/hr; continue distillation until 100 ml of water collects

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Discontinue the distillation, cool the flask partially, transfer the contents to a 125–250 ml separating funnel, and drain

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Rinse the flask with 15 ml of alcohol and again with 18 ml of alcohol, and warm if necessary to dissolve any residue; transfer the rinsings to a tared 150 ml beaker

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Allow the liquid in the separating funnel to cool, and extract with 25 ml, and then with 20 ml of chloroform — if there is a tendency for emulsification, add one or two drops of dilute HCl (1 + 2)

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Transfer the chloroform extracts to the tared beaker containing the alcohol washings

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Extract the residual aqueous phase in the separating funnel once with 25 ml of ether, and add the ether extract to the others in the tared beaker

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Evaporate the combined extracts carefully by keeping the beaker on the cover of the boiling water bath until the ether and the chloroform layers are removed; thereafter evaporate the residual liquid on an open water bath

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After evaporation is complete, allow the beaker to remain on the water bath for a further 15 min or until no odour of alcohol remains

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Wipe the outside of the beaker dry, allow to cool, and weigh; reheat, cool and weigh until the loss in weight is less than 2 mg for a 5 min heating period

Calculation

% Residue by steam distillation = (Wt of residue × 100) / Wt of sample

Where,

• Wt of residue = weight of the dried residue in the tared beaker
• Wt of sample = weight of the oil taken (from the weighed 15 ml pipetting)

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., 1975, p. 340.