Ethylene Glycol Stearates - Definition, Identification, Impurities - USP 2025

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

Ethylene Glycol Stearates is a mixture of ethylene glycol monoesters and diesters of stearic and palmitic acids. It contains NLT 50.0% of monoesters produced from the condensation of ethylene glycol and stearic acid of vegetable or animal origin.

2 IDENTIFICATION

• A. It meets the requirements in Specific Tests for Melting Range or Temperature, Class II 〈741〉.

• B. It meets the requirements in Specific Tests for Fats and Fixed Oils, Fatty Acid Composition 〈401〉.

3 ASSAY

• Procedure

Mobile phase: Tetrahydrofuran

Sample solution: 40 mg/mL of Ethylene Glycol Stearates in tetrahydrofuran

3.1 Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: Refractive index

Column: 7.5-mm × 60-cm; containing 5-µm 100Å packing L21.

[Note—Two or three 7.5-mm × 30-cm L21 columns may be used in place of the one 60-cm column, provided that System suitability requirements are met.]

Temperatures

Column: 40°.

[Note—The column temperature may be lowered to ambient temperature, although working at 40° provides stable separation conditions and ensures better sample solubility.]

Detector: 40°

Flow rate: 1 mL/min

Injection volume: 40 µL

3.2 System suitability

Sample: Sample solution

[Note—The relative retention times for diesters, monoesters, and ethylene glycol are 0.76, 0.83, and 1.0, respectively.]

Suitability requirements

Relative standard deviation: NMT 2.0% for the monoesters peak

3.3 Analysis

Sample: Sample solution

Calculate the percentage of free fatty acids, E, in the portion of Ethylene Glycol Stearates taken:

E = I × 270 / 561.1

I = acid value, determined in Specific Tests for Fats and Fixed Oils, Acid Value (Free Fatty Acids) 〈401〉

Calculate the percentage of monoesters in the portion of Sample taken:

Result = [ rₘ / (rₘ + r_d) ] (100 − D − E)

rₘ = peak response for the monoesters

r_d = peak response for the diesters

D = percentage of free ethylene glycol in the portion of Ethylene Glycol Stearates taken, as determined in Impurities for Limit of Free Ethylene Glycol

Acceptance criteria: NLT 50.0% of monoesters

4 IMPURITIES

• Limit of Free Ethylene Glycol

Mobile phase, Sample solution, Chromatographic system, and System suitability: Proceed as directed in the Assay.

Standard solution A: 0.5 mg/mL of ethylene glycol in tetrahydrofuran

Standard solution B: 1.0 mg/mL of ethylene glycol in tetrahydrofuran

Standard solution C: 2.0 mg/mL of ethylene glycol in tetrahydrofuran

Standard solution D: 4.0 mg/mL of ethylene glycol in tetrahydrofuran

Analysis

Samples: Sample solution and Standard solutions

Plot the ethylene glycol peak responses obtained versus the concentration of ethylene glycol in the Standard solutions. From the standard curve so obtained, determine the ethylene glycol concentration in the Sample solution.

Calculate the percentage of free ethylene glycol in the portion of sample taken:

Result = (C / Cₛ) × 100

C = concentration of ethylene glycol, determined from the standard curve (mg/mL)

Cₛ = concentration of the Sample solution (mg/mL)

Acceptance criteria: NMT 5.0%

5 SPECIFIC TESTS

• Melting Range or Temperature, Class II 〈741〉: 54°–60°

• Fats and Fixed Oils, Acid Value (Free Fatty Acids) 〈401〉

Sample: 10.0 g

Acceptance criteria: NMT 3.0

• Fats and Fixed Oils, Iodine Value 〈401〉: NMT 3.0

• Fats and Fixed Oils, Saponification Value 〈401〉

Sample: 2.0 g

Acceptance criteria: 170–195

• Fats and Fixed Oils, Fatty Acid Composition 〈401〉:

40.0%–60.0% of stearic acid, and the sum of palmitic and stearic acids is NLT 90.0%.

• Articles of Botanical Origin, Total Ash 〈561〉

Sample: 1.0 g

Acceptance criteria: NMT 0.1%

6 ADDITIONAL REQUIREMENTS

• Packaging and Storage: Preserve in tight containers. No storage requirements specified.

• Labeling: Label it to indicate that it is intended for topical use only.