Propylene Glycol Monolaurate

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 Dodecanoic acid, monoester with 1,2-propanediol; 

Lauric acid, monoester with propane-1,2-diol. 

2 DEFINITION 

Propylene Glycol Monolaurate is a mixture of the propylene glycol mono- and diesters of lauric acid. The requirements for monoester and diester content differ for the two types of Propylene Glycol Monolaurate, as set forth in the table below. 

3 IDENTIFICATION 

A. Thin-Layer Chromatographic Identification Test 〈201〉 

Standard solution: 50 mg/mL of USP Propylene Glycol Monolaurate Type I RS (or USP Propylene Glycol Monolaurate Type II RS) in methylene chloride 

Sample solution: 50 mg/mL in methylene chloride 

Chromatographic system 

(See Chromatography 〈621〉, Thin-Layer Chromatography.) 

Developing solvent system: Ether and hexane (70:30) 

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

Analysis: 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 from the Sample solution correspond to those from the Standard solution. B. It meets the requirements in Specic Tests for Fats and Fixed Oils, Fatty Acid Composition〈401〉. 

4 ASSAY 

Procedure 

Mobile phase: Tetrahydrofuran 

Sample solution: 40 mg/mL of Propylene Glycol Monolaurate in tetrahydrofuran 

Chromatographic system 

(See Chromatography 〈621〉, System Suitability.) 

Mode: LC 

Detector: Refractive index 

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

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

Column: 40° 

Detector: 40° 

Flow rate: 1 mL/min 

Injection volume: 40 µL 

System suitability 

Sample: Sample solution 

Suitability requirements 

[Note—The order of elution is diesters, monoesters, and propylene glycol.] 

Relative standard deviation: NMT 1.0% for the monoester peak 

Analysis 

Sample: Sample solution 

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

Result = (r_U/r_T) × (100 − D)  

r_U = peak response for monoesters or diesters 

r_T = sum of the peak responses of the monoesters and diesters  

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 in the portion taken: 

Result = (A/561.1) × 200 

A = acid value 

Acceptance criteria 

Type I

Monoesters: 45.0%–70.0% 

Diesters: 30.0%–55.0% 

Type II 

Monoesters: NLT 90.0% 

Diesters: NMT 10.0% 

5 IMPURITIES 

Limit of Propylene Glycol 

Mobile phase, Sample solution, and Chromatographic system: 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 asks 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 fth 15-mL ask, introduce 5.0 mL of Standard stock solution. 

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 of propylene glycol in the Sample solution from the standard curve. 

Calculate the percentage of free propylene glycol in the portion of Propylene Glycol Monolaurate taken: 

Result = (C/C_U) × 100  

C = concentration of propylene glycol in the Sample solution from the standard curve 

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

Acceptance criteria 

Propylene glycol monolaurate (Type I): NMT 5.0% 

Propylene glycol monolaurate (Type II): NMT 1.0% 

6 SPECIFIC TESTS 

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

Fats and Fixed Oils, Fatty Acid Composition〈401〉: Propylene Glycol Monolaurate exhibits the composition prole of fatty acids shown in Table 1. 

Table 1 

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

Fats and Fixed Oils, Saponification Value〈401〉 

Propylene glycol monolaurate (Type I): 210–245 

Propylene glycol monolaurate (Type II): 200–230 

Water Determination, Method Ia〈921〉 

Analysis: Use a mixture of methanol and methylene chloride (1:1) in place of methanol in the titration vessel. 

Acceptance criteria: NMT 1.0% 

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

7 ADDITIONAL REQUIREMENTS 

Packaging and Storage: Preserve in well-closed containers, and protect from moisture. No storage requirements specied. Labeling: Label it to indicate the type (Type I or Type II). 

USP Reference Standards 〈11〉 

USP Propylene Glycol RS 

USP Propylene Glycol Monolaurate Type I RS 

USP Propylene Glycol Monolaurate Type II RS 

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