Rubbing Alcohol

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

Rubbing Alcohol and all preparations under the classification of Rubbing Alcohols are manufactured in accordance with the requirements of the U.S. Treasury Department, Bureau of Alcohol, Tobacco, and Firearms, Formula 23-H (8 parts by volume of acetone, 1.5 parts by volume of methyl isobutyl ketone, and 100 parts by volume of ethyl alcohol) being used. It contains NLT 68.5% and NMT 71.5% by volume of dehydrated alcohol, the remainder consisting of water and the denaturants, with or without color additives, and perfume oils. Rubbing Alcohol contains, in each 100 mL, NLT 355 mg of sucrose octaacetate or NLT 1.40 mg of denatonium benzoate. The preparation may be colored with one or more color additives, listed by the FDA for use in drugs. A suitable stabilizer may be added. Rubbing Alcohol complies with the requirements of the Bureau of Alcohol, Tobacco, and Firearms of the U.S. Treasury Department.

[Note—Rubbing Alcohol is packaged, labeled, and sold in accordance with the regulations issued by the U.S. Treasury Department, Bureau of Alcohol, Tobacco, and Firearms.]

2 ASSAY

2.1 Denatonium Benzoate

Buffer: 9.23 g of anhydrous dibasic sodium phosphate in 800 mL of water. Adjust with saturated citric acid solution to a pH of 4 ± 0.1, dilute with water to 1000 mL, and mix.

Standard solution: 50 µg/mL of USP Denatonium Benzoate RS in water

Sample solution: Dissolve the residue obtained in the test for Limit of Nonvolatile Residue in 50.0 mL of water, and transfer to a suitable flask.

Instrumental conditions

Analytical wavelength: Maximum absorbance at about 410 nm

Cell: 1 cm

Analysis

Samples: Buffer, Standard solution, and Sample solution

Transfer 10.0 mL each of Buffer, Standard solution, and Sample solution to individual 250-mL separators. Add to each 40 mL of Buffer, 10 mL of a 1-in-1000 solution of bromophenol blue in chloroform, and 60 mL of chloroform. Shake the separators vigorously for 2 min, allow to stand for 15 min, then withdraw the chloroform layers through chloroform-washed cotton into 100-mL volumetric flasks.

Repeat the extraction with 20 mL of chloroform, adding the filtered chloroform extracts to the respective volumetric flasks, and dilute with chloroform to volume. Without delay, concomitantly determine the absorbances of the solutions, using the blank to set a suitable spectrophotometer.

Calculate the quantity, in mg, of denatonium benzoate (C₂₈H₃₄N₂O₃ · H₂O) in 100 mL of Rubbing Alcohol:

Result = (A_U/A_S) × C × 0.025

A_U = absorbance of the Sample solution

A_S = absorbance of the Standard solution

C = concentration of USP Denatonium Benzoate RS in the Standard solution (µg/mL)

Acceptance criteria: NLT 1.40 mg

2.2 Sucrose Octaacetate

Sample solution: Using about 50 mL of 70% alcohol, transfer the residue obtained in the test for Limit of Nonvolatile Residue to a 500-mL conical flask.

Analysis: Neutralize the Sample solution with 0.1 N sodium hydroxide VS, using phenolphthalein TS as the indicator. Add 25.0 mL of 0.1 N sodium hydroxide, attach an air condenser to the flask, and reflux on a steam bath for 1 h. Remove from the steam bath, cool quickly, and titrate the excess alkali with 0.1 N sulfuric acid VS, using phenolphthalein TS as the indicator. Perform a blank determination (see Titrimetry 〈541〉, Residual Titrations). Each mL of 0.1 N sodium hydroxide is equivalent to 8.483 mg of sucrose octaacetate (C₂₈H₃₈O₁₉).

Acceptance criteria: NLT 355 mg of sucrose octaacetate per 100 mL of Rubbing Alcohol

3 IMPURITIES

3.1 Methanol

Sample solution: Dilute 0.50 mL of Rubbing Alcohol with water to 1.0 mL.

Analysis: To 0.50 mL of the Sample solution add 1 drop of dilute phosphoric acid (1 in 20) and 1 drop of potassium permanganate solution (1 in 20). Mix, allow to stand for 1 min, and add dropwise sodium metabisulfite solution (1 in 20) until the permanganate color is discharged. If a brown color remains, add 1 drop of dilute phosphoric acid (1 in 20). To the colorless solution add 5 mL of freshly prepared chromotropic acid TS, and heat in a water bath at 60° for 10 min.

Acceptance criteria: No violet color appears.

4 SPECIFIC TESTS

Specific Gravity 〈841〉: 0.8691–0.8771 at 15.56° (the U.S. government standard temperature for alcohol determination) for Rubbing Alcohol manufactured with specially denatured alcohol Formula 23-H

Limit of Nonvolatile Residue

Where the denaturant is denatonium benzoate

Sample: 200.0 mL of Rubbing Alcohol

Analysis: Evaporate the Sample, transferred in convenient portions, in a suitable tared dish on a steam bath, and dry the residue at 105° for 1 h. Retain the residue for the Assay for Denatonium Benzoate.

Acceptance criteria: The weight of the residue is NLT 2.8 mg.

Where the denaturant is sucrose octaacetate

Sample: 25.0 mL of Rubbing Alcohol

Analysis: Evaporate the Sample in a suitable tared dish on a steam bath, and dry the residue at 105° for 1 h. Retain the residue for the Assay for Sucrose Octaacetate.

Acceptance criteria: The weight of the residue is NLT 89 mg.

5 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers, remote from fire, and store at controlled room temperature.

Labeling: Label it to indicate that it is flammable.

USP Reference Standards 〈11〉

USP Denatonium Benzoate RS