Light Mineral Oil
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This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition
Issued and maintained by the United States Pharmacopeial Convention (USP)
1 DEFINITION
Light Mineral oil is a purified mixture of liquid hydrocarbons obtained from petroleum. It may contain a suitable stabilizer.
2 IDENTIFICATION
Change to read:
A. Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197F (CN 1-May-2020)
B. It meets the requirements in Specific Tests for Viscosity - Capillary Methods 〈911〉.
3 IMPURITIES
Limit of Polycyclic Aromatic Hydrocarbons
Dimethyl sulfoxide: Use spectrophotometric grade dimethyl sulfoxide.
n-Hexane: Use n-hexane that has been washed by being shaken previously twice with one-fifth its volume of Dimethyl sulfoxide.
Standard solution: 7.0 μg/mL of USP Naphthalene RS in isooctane (2,2,4-trimethylpentane)
Standard blank: 2,2,4-Trimethylpentane
Sample solution: Transfer 25.0 mL of Light Mineral Oil and 25 mL of n-Hexane to a 125-mL separator, and mix. [Note—Use no lubricants other than water on the stopcock, or use a separator equipped with a suitable polymeric stopcock.]
Add 5.0 mL of Dimethyl sulfoxide, and shake the mixture vigorously for 1 min. Allow to stand until the lower layer is clear, transfer the lower layer to another 125-mL separator, add 2 mL of n-Hexane, and shake vigorously. Use the lower layer.
Sample blank: Dimethyl sulfoxide that has been shaken previously vigorously for 1 min with n-Hexane in the ratio of 5 mL of Dimethyl sulfoxide to 25 mL of n-Hexane
Instrumental conditions
(See Ultraviolet-Visible Spectroscopy 〈857〉.)
Mode: UV
Analytical wavelengths
Standard solution: 275 nm
Sample solution: 260–350 nm
Cell: 1 cm
Analysis
Samples: Standard solution, Standard blank, Sample solution, and Sample blank
Acceptance criteria: The absorbance at any wavelength in the specified range of the Sample solution is NMT one-third of the absorbance of the Standard solution.
4 SPECIFIC TESTS
Specific Gravity 〈841〉: 0.818–0.880
Viscosity - Capillary Methods 〈911〉: 3.0–34.4 mm2 · s−1 for kinematic viscosity, measured with a capillary viscometer at 40 ± 0.1°
Acidity
Sample solution: Combine 10 mL of Light Mineral Oil and 20 mL of boiling water, shake vigorously for 1 min, and allow to cool. Remove, and filter the aqueous layer.
Analysis: To 10 mL of the Sample solution add 0.1 mL of phenolphthalein TS.
Acceptance criteria: The solution does not produce a pink color. NMT 1.0 mL of 0.01 N sodium hydroxide is required to produce a pink color.
Readily Carbonizable Substances Test 〈271〉
Sample: 5 mL
Standard solution: In a glass-stoppered test tube that previously has been rinsed with hot nitric acid (see Cleaning Glass Apparatus 〈1051〉), mix 3 mL of ferric chloride CS, 1.5 mL of cobaltous chloride CS, and 0.5 mL of cupric sulfate CS then overlaid with 5 mL of Light Mineral Oil.
Analysis: Place the Sample in a glass-stoppered test tube that previously has been rinsed with hot nitric acid (see Cleaning Glass Apparatus 〈1051〉), then rinsed with water, and dried. Add 5 mL of sulfuric acid containing 94.5%–94.9% of H SO , and heat in a boiling water bath for 10 min. After the test tube has been in the bath for 30 s, remove it quickly, and, while holding the stopper in place, give three vigorous, vertical shakes over an amplitude of about 5 in. Repeat every 30 s. Do not keep the test tube out of the bath longer than 3 s for each shaking period. At the end of 10 min from the time when first placed in the water bath, remove the test tube.
Acceptance criteria: The oil portion of the Sample may turn hazy, but it remains colorless or shows a slight pink or yellow color, and the acid portion of the Sample does not become darker than the Standard solution.
Solid Paraffin
Sample: Light Mineral Oil that has been dried previously in a beaker at 105° for 2 h and cooled to room temperature in a desiccator over silica gel
Analysis: Fill a tall, cylindrical, standard oil-sample bottle of colorless glass of 120-mL capacity with the Sample. Insert the stopper, and immerse the bottle in a mixture of ice and water for 4 h.
Acceptance criteria: The Sample is su
ciently clear that a black line 0.5 mm in width, on a white background, held vertically behind the bottle, is clearly visible.
Limit of Sulfur Compounds
Solution A: Saturated solution of lead(II) oxide in sodium hydroxide (200 mg/mL)
Sample: 4.0 mL
Analysis: Combine the Sample, 2 mL of dehydrated alcohol, and 2 drops of Solution A, heat at 70° for 10 min with frequent shaking, and cool.
Acceptance criteria: No dark brown color develops.
5 ADDITIONAL REQUIREMENTS
Packaging and Storage: Preserve in tight, light-resistant containers. No storage requirements specified.
Labeling: Label it to indicate the name and quantity of any substance added as a stabilizer, and label packages intended for direct use by the public to indicate that it is not intended for internal use.
USP Reference Standards 〈11〉
USP Mineral Oil RS
