Lemon Oil

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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1 DEFINITION

Lemon Oil is the volatile oil obtained by expression, without the aid of heat, from the fresh peel of the fruit of Citrus x limon (L.) Osbeck (Fam. Rutaceae), with or without the previous separation of the pulp and the peel. The total aldehyde content, calculated as citral (C₁₀H₁₆O), is NLT 2.2% and NMT 3.8% for California-type Lemon Oil, and NLT 3.0% and NMT 5.5% for Italian-type Lemon Oil.

[Note—Do not use Lemon Oil that has a terebinthine odor.]

2 ASSAY

Total Aldehyde Content

Reagent solution: Dissolve 4.5 g of hydroxylamine hydrochloride in 13 mL of water. Add 85 mL of tertiary butyl alcohol, mix, and adjust with 0.5 N potassium hydroxide to a pH of 3.4.

Sample: 5 mL

Analysis: Pipet 50 mL of the Reagent solution into a conical flask containing the Sample. Insert the stopper in the flask, and allow to stand at room temperature for 30 min, with occasional shaking. Titrate the liberated hydrochloric acid with 0.5 N alcoholic potassium hydroxide VS to a pH of 3.4. Each mL of 0.5 N alcoholic potassium hydroxide consumed in the titration is equivalent to 76.12 mg of total aldehydes, calculated as citral (C₁₀H₁₆O).

Acceptance criteria: The total aldehyde content, calculated as citral (C₁₀H₁₆O), is 2.2%–3.8% for California-type Lemon Oil or 3.0%–5.5% for Italian-type Lemon Oil.

3 SPECIFIC TESTS

Specific Gravity 〈841〉: 0.849–0.855

Optical Rotation, Angular Rotation 〈781A〉: +57° to +65.6°

efractive Index 〈831〉: 1.473–1.476 at 20°

Ultraviolet Absorbance

Sample solution: Dilute 250 mg of Oil to 100 mL with alcohol

Blank: Alcohol

Instrumental conditions

(See Ultraviolet-Visible Spectroscopy 〈857〉.)

Mode: UV-Vis

Spectral range: 260–400 nm

Analysis

Samples: Sample solution and Blank

Record the spectrum in a 1-cm cell, and determine the absorbance at the wavelength of maximum absorbance at about 315 nm using the line drawn tangent to the curves appearing as minima in the spectrum in wavelength regions above and below the maximum wavelength as the baseline.

Acceptance criteria: The absorbance, calculated on the basis of a 250-mg specimen, is NLT 0.20 for California-type Lemon Oil or NLT 0.49 for Italian-type Lemon Oil.

Foreign Oils: Place 50 mL of Oil in a four-bulb Ladenburg flask having the following dimensions: the lower or main bulb is about 6 cm in diameter, and the smaller condensing bulbs are about 3.5, 3.0, and 2.5 cm in diameter; the distance from the bottom of the flask to the side-arm is about 20 cm. Distill Oil at a rate of 1 drop/s until the distillate measures 5 mL: the angular rotation of the first 5 mL is NMT 6° less than that of the original Oil. The refractive index at 20° of this same portion is 0.001–0.003 lower than that of the original Oil.

4 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-filled, tight containers, and avoid exposure to excessive heat.

Labeling: The label states the Latin binomial and, following the official name, the part of the plant source from which the article was derived. Label it to also indicate whether it is California-type or Italian-type Lemon Oil. The label indicates that Oil is not to be used if it has a terebinthine odor.