SOP: Aldehyde Content in Essential Oils
GIFSQ — Global Institute for Food Safety & Quality
Principle
Aldehydes react with hydroxylamine hydrochloride to liberate acid, which is titrated with standard hydrochloric acid using bromophenol blue indicator; the difference between the blank and sample titres is converted to aldehyde content with the factor given for the oil (citral or decanal).
Apparatus required
- Glass-stoppered conical flasks
Reagents
a. Bromophenol blue indicator: to 0.1 g of the indicator, add 3.0 ml of 0.05 N NaOH with trituration, and dilute to 25 ml with distilled water when the solution is complete.
b. Hydroxylamine hydrochloride (H₂NOH·HCl) solution: dissolve 20 g in 40 ml of distilled water, dilute to 400 ml with alcohol, and add with stirring 300 ml of 0.5 N alcoholic KOH solution and 2.5 ml of the bromophenol blue solution.
c. 0.5 N alcoholic KOH solution: dissolve 28.06 g of KOH in 60% alcohol, and dilute to 1000 ml with 60% alcohol.
d. 0.5 N HCl solution.
Procedure
Accurately weigh the sample as shown in the table below
↓
Add 75 ml of the hydroxylamine solution, and mix thoroughly
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Allow to stand at room temperature for the time shown in the table
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Titrate to the greenish-yellow end point of bromophenol blue using 0.5 N HCl
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Carry out a blank determination using 75 ml of hydroxylamine solution
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Subtract the sample titre from the blank titre, and calculate the aldehyde content in the sample using the factor given in the table
| Oil | Sample size | Reaction time (min) | Factor for 1 ml of 0.5 N KOH |
|---|---|---|---|
| Lemon oil, Arizona | 5.0 g | — | 0.07612 |
| Lemon oil, distilled | 5.0 ml | 60 | 0.07612 |
| Lime oil, cold pressed | 5.0 ml | 60 | 0.07612 |
| Orange oil, distilled | 5.0 ml | 60 | 0.07814 |
| Tangerine oil, cold pressed | 5.0 ml | 60 | 0.07814 |
| Mandarin oil, cold pressed | 5.0 ml | 60 | 0.07814 |
| Bitter orange oil, cold pressed | 10.0 ml | 30 | 0.07814 |
Calculation
Aldehyde % = ((Blank titre − Sample titre) × Factor × 100) / Wt of sample
Where,
- Blank titre = ml of 0.5 N HCl used in the blank titration
- Sample titre = ml of 0.5 N HCl used in the sample titration
- Factor = 0.07612 (citral) or 0.07814 (decanal), grams of aldehyde per ml of 0.5 N reagent, as given in the table
- Wt of sample = weight of the oil taken
The weight of sample should be such that the ml of 0.5 N HCl required for the titration of the sample is more than half the volume required to titrate the blank.
Precautions
- The titre value of fresh hydroxylamine solution prepared as stated is approximately 30 ml; the weights indicated are based on this. On standing for more than 10 days, the solution has a tendency to lose strength.
References
Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.
- Winkler, W.O., J. Assoc. Offic. Anal. Chem., 36, 119 (1953).
- EOA Specifications and Standards, Essential Oil Association of USA, Inc.: Determinations 1-1.