Propylene Glycol Dilaurate

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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C₂₇H₅₂O₄

Lauric acid, diester with propane-1,2-diol;

Propane-1,2-diyl didodecanoate

440.70  CAS RN^®: 22788-19-8.

1 DEFINITION

Propylene Glycol Dilaurate is a mixture of the propylene glycol mono- and diesters of lauric acid. It contains NLT 70.0% of diesters and NMT 30.0% of monoesters.

2 IDENTIFICATION

2.1 A. Thin-Layer Chromatographic Identification Test 〈201〉

Standard solution: 50 mg/mL of USP Propylene Glycol Dilaurate RS in methylene chloride

Sample solution: 50 mg/mL of Propylene Glycol Dilaurate in methylene chloride

Developing solvent system: Hexane and ether (3:7)

Spray reagent: 0.1 mg/mL of rhodamine 6G in alcohol

Analysis: Apply 200 µg of the Standard solution and Sample solution. Develop the chromatogram over a path of 15 cm, and dry the plate in a current of air. Spray the plate with Spray reagent, and locate the spots on the plate by examination under UV light at a wavelength of 365 nm.

Acceptance criteria: The R values of the principal spots of the Sample solution correspond to those of the Standard solution.

2.2 B. Fats and Fixed Oils, Fatty Acid Composition 〈401〉: Meets the requirements

3 ASSAY

3.1 Procedure

Mobile phase: Tetrahydrofuran

Sample solution: 200 mg of Propylene Glycol Dilaurate in 5 mL of tetrahydrofuran

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: Refractive index

Column: 7-mm × 60-cm; 5-µm packing L21 (100Å)

[Note—Two 7-mm × 30-cm L21 columns may be used in place of one 60-cm column, provided system suitability requirements are met.]

Temperature

Column: 40°

Detector: 40°

Flow rate: 1 mL/min

Injection size: 40 µL

System suitability

Sample: Sample solution

[Note—Elution order: diesters, monoesters, propylene glycol.]

Suitability requirements

Relative standard deviation: NMT 1.0% is determined from the monoester peak.

Analysis

Sample: Sample solution

Calculate the percentage of monoesters or diesters in the portion of Propylene Glycol Dilaurate taken:

Result = (r_U/r_T) × (100 − D)

r_U = peak response for monoesters or diesters

r_T = sum of the responses of the monoester and diester peaks

D = sum of the percentage content of propylene glycol and the percentage content of free fatty acids

Calculate the percentage content of free fatty acids:

Result = (A/561.1) × 200

A = acid value

Acceptance criteria: NLT 70.0% of diesters and NMT 30.0% of monoesters

4 IMPURITIES

4.1 Inorganic Impurities

Articles of Botanical Origin, Total Ash 〈561〉: NMT 0.1%

4.2 Organic Impurities

Procedure: Limit of Propylene Glycol

Mobile phase: Proceed as directed in the Assay.

Standard stock solution: 4 mg/mL of USP Propylene Glycol RS in tetrahydrofuran

Standard solutions: Into four 15-mL flasks, introduce respectively 0.25, 0.5, 1.0, and 2.5 mL of Standard stock solution, and dilute with tetrahydrofuran to 5.0 mL. In a fifth 15-mL flask, introduce 5.0 mL of Standard stock solution.

Sample solution: Use the Sample solution from the Assay.

Chromatographic system: Proceed as directed in the Assay.

Analysis

Samples: Standard solutions and Sample solution

Prepare a standard curve of peak area versus concentration, in mg/mL, of propylene glycol in the Standard solutions. Obtain the concentration, C, in mg/mL, of propylene glycol in the Sample solution from the standard curve.

Acceptance criteria: NMT 2.0% of propylene glycol is found.

5 SPECIFIC TESTS

Fats and Fixed Oils, Acid Value 〈401〉: NMT 4

Fats and Fixed Oils, Fatty Acid Composition 〈401〉: Propylene Glycol Dilaurate exhibits the following composition profile of fatty acids, determined as directed in the chapter.

Fats and Fixed Oils, Iodine Value 〈401〉: NMT 1

Fats and Fixed Oils, Saponification Value 〈401〉: 230–250

Water Determination, Method Ia 〈921〉: NMT 1.0%, using a mixture of methanol and methylene chloride (1:1) in place of methanol in the titration vessel

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers, and protect from moisture. No storage requirements are specified.

USP Reference Standards 〈11〉

USP Propylene Glycol RS

USP Propylene Glycol Dilaurate RS