Dimethyl Sulfoxide

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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C₂H₆OS  78.13

Methane, sulfinylbis-;

Methyl sulfoxide   CAS RN®: 67-68-5; UNII: YOW8V9698H.

1 DEFINITION

Dimethyl sulfoxide contains NLT 99.9% of dimethyl sulfoxide (C₂H₆OS), calculated on the anhydrous basis.

2 IDENTIFICATION

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A. Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197A or 197F. Potassium bromide plates are used for 197F. 

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B. The retention time of the major peak of the Sensitivity solution corresponds to that of the major peak of the Sample solution, as obtained under the test for Organic Impurities.

3 ASSAY

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3.1 Procedure

Analysis: Using the results from the tests for Limit of Nonvolatile Residue and Organic Impurities, calculate the percentage of dimethyl sulfoxide (C₂H₆OS) in the portion of Dimethyl Sulfoxide taken:

Result = 100 − I

I = sum of the percentage of nonvolatile residue as determined in the Limit of Nonvolatile Residue test and the percentage of total impurities as determined in the Organic Impurities test

Acceptance criteria: NLT 99.9% on the anhydrous basis

4 IMPURITIES

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4.1 Organic Impurities

Diluent: Methanol

System suitability solution: 1 mg/mL of USP Dimethyl Sulfoxide RS and 10 µg/mL of USP Methylsulfonylmethane RS in Diluent

Sensitivity solution: 30 µg/mL of USP Dimethyl Sulfoxide RS in Diluent

Sample solution: 100 mg/mL of Dimethyl Sulfoxide in Diluent

Chromatographic system

• (See Chromatography 〈621〉, System Suitability.)
• Mode: GC
• Detector: Flame ionization
• Column: 0.53-mm × 30-m capillary column coated with a 3-µm film of phase G43
• Temperatures
• Injection port: 250°
• Detector: 250°
• Column: See Table 1.

Table 1

Carrier gas: Hydrogen

Flow rate: 5 mL/min

Injection volume: 0.5 µL

Injection type: Split, split ratio 10:1

System suitability

• Samples: System suitability solution and Sensitivity solution
• [Note-The relative retention times for dimethyl sulfoxide and methylsulfonylmethane are 1.0 and 1.6, respectively. These relative retention times are provided as information that could aid in peak assignment.]
• Suitability requirements
• Resolution: NLT 4.0 between dimethyl sulfoxide and methylsulfonylmethane, System suitability solution
• Relative standard deviation: NMT 5.0%, Sensitivity solution
• Signal-to-noise ratio: NLT 10, Sensitivity solution

Analysis

Sample: Sample solution

Calculate the percentage of total impurities in the portion of Dimethyl Sulfoxide taken:

Result = (r_u/r_T) × 100

r_u = sum of the areas of all the impurity peaks in the Sample solution

r_T = sum of the areas of all peaks in the Sample solution

Acceptance criteria: The reporting threshold is 0.03%.

Total impurities: NMT 0.1% 

4.2 Limit of Nonvolatile Residue

Sample: 100.0 g of Dimethyl Sulfoxide

Analysis: Evaporate the Sample to dryness in a tared, preconditioned dish on a hot plate under a suitable fume hood. Evaporate gently so that boiling does not occur.

Acceptance criteria: The weight of the residue is NMT 0.01%.

5 SPECIFIC TESTS

5.1 Specific Gravity 〈841〉: 1.095–1.101

5.2 Refractive Index 〈831〉: 1.4755–1.4775

5.3 Acidity

Sample solution: 500 mg/mL of Dimethyl Sulfoxide in water

Analysis: To the Sample solution, add phenolphthalein TS. If the solution remains colorless, titrate with 0.01 N sodium hydroxide VS until a pink color appears.

Acceptance criteria: NMT 5.0 mL of 0.01 N sodium hydroxide is consumed.

5.4 Water Determination 〈921〉, Method I

Analysis: Weigh and transfer the test specimen in an environment of low humidity to minimize absorption of atmospheric water.

Acceptance criteria: NMT 0.1%

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5.5 Ultraviolet Absorbance

Instrumental conditions

• (See Ultraviolet-Visible Spectroscopy 〈857〉.)
• Mode: UV
• Spectral range: 270–350 nm
• Cell: 1 cm
• Blank: Water

Analysis: Maintain Dimethyl Sulfoxide in a water bath at a temperature of less than 20°. [Note-Do not freeze.] Purge with dry nitrogen for 30 min.

Acceptance criteria: The spectrum is smooth with no absorption maxima; the absorbance at 275 nm is NMT 0.20, and the absorbance ratio of A₂₈₅/A₂₇₅ at the wavelengths indicated by the subscripts is NMT 0.65 and of A₂₉₅/A₂₇₅ at the wavelengths indicated by the subscripts is NMT 0.45.

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight, light-resistant containers.

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USP Reference Standards 〈11〉

USP Dimethyl Sulfoxide RS

USP Methylsulfonylmethane RS