Glyceryl Monostearate

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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Octadecanoic acid, monoester with 1,2,3-propanetriol;

Monostearin

CAS RN®: 31566-31-1.

1 DEFINITION

Glyceryl Monostearate contains NLT 90.0% of monoglycerides of saturated fatty acids, chiefly glyceryl monostearate (C₂₁H₄₂O₄) and glyceryl monopalmitate (C₁₉H₃₈O₄). It may contain a suitable antioxidant.

2 ASSAY

Procedure

Mobile phase: Tetrahydrofuran

Sample solution: 8 mg/mL of Glyceryl Monostearate in tetrahydrofuran

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: Refractive index

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

Temperature: Column and detector temperatures are maintained at 40°.

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

Flow rate: 1 mL/min

Injection size: 40 µL

System suitability

Sample: Sample solution

[Note—The relative retention times for triglycerides, diglycerides, monoglycerides, and Glycerin are 0.77, 0.81, 0.86, and 1.0, respectively.] Suitability requirements

Relative standard deviation: NMT 2.0%, determined from the monoglycerides peak

Analysis

Sample: Sample solution

Calculate the percentage of monoglycerides in the portion of Glyceryl Monostearate taken:

Result = (r_U/r_T) × 100

r_U = peak response of the monoglycerides

r_T = sum of all the glyceride peak responses

Acceptance criteria: NLT 90.0% of monoglycerides of saturated fatty acids, chiefly C₂₁H₄₂O₄ and  C₁₉H₃₈O₄

3 IMPURITIES

Inorganic Impurities

Residue on Ignition 〈281〉: NMT 0.5%

Organic Impurities

Procedure: Limit of Free Glycerin

Propionating reagent: Pyridine and propionic anhydride (1:2)

Internal standard solution: 0.2 mg/mL of tributyrin in chloroform

Standard solution: Transfer 15 mg of glycerin and 50 mg of tributyrin to a glass-stoppered, 25-mL conical ask. Add 3 mL of Propionating reagent, and heat at 75° for 30 min. Volatilize the reagents with the aid of a stream of nitrogen at room temperature, and add 12 mL of chloroform. Dilute 1 mL of this mixture with chloroform to 20 mL.

Sample solution: Transfer 50 mg of Glyceryl Monostearate to a glass-stoppered, 25-mL conical ask. Add 5 mL of Internal standard solution by pipet, and mix to dissolve. Immerse the ask in a water bath, maintained at a temperature between 45° and 50°, and volatilize the chloroform with the aid of a stream of nitrogen. Add 3 mL of Propionating reagent, and heat at 75° for 30 min. Volatilize the reagents with the aid of a stream of nitrogen at room temperature, and add 5 mL of chloroform.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: GC

Detector: Flame ionization (under typical conditions)

Column: 4-mm × 2.4-m borosilicate glass, packed with 2% liquid phase G16, on 80- to 100-mesh support S1A

Temperature

Injector: 300°

Detector: 310°

Column: The column is maintained isothermally at a temperature between 190° and 200°.

Carrier gas: Helium

Flow rate: 70 mL/min

System suitability

Sample: Standard solution (6–10 injections)

Suitability requirements

Resolution: NLT 4.0 between derivatized glycerin and tributyrin

Relative standard deviation: NMT 2.0% of the ratio of their peak areas

Analysis

Samples: Standard solution and Sample solution

Calculate the response factor, F:

F = (A_D/A_S) × (W_S/W_D)

A_D = peak area of tributyrin from the Standard solution

A_S = peak area of tripropionin from the Standard solution

W_S = weight of glycerin in the Standard solution (mg)

W_D = weight of tributyrin in the Standard solution (mg)

Calculate the percentage of glycerin in the portion of Glyceryl Monostearate taken:

Result = (A_U/A_S) × (W_D/W_U) × F × 100

A_U = peak area of tripropionin in the Sample solution

A_S = peak area of tributyrin in the Sample solution

W_D = weight of tributyrin in 5 mL of Internal standard solution (mg)

W_U = weight of Glyceryl Monostearate in the Sample solution (mg)

Acceptance criteria: NMT 1.2%

4 SPECIFIC TESTS

Melting Range or Temperature, Class I 〈741〉: Does not melt below 55°

Fats and Fixed Oils, Acid Value 〈401〉: NMT 6

Fats and Fixed Oils, Hydroxyl Value 〈401〉: 290–330

Fats and Fixed Oils, Iodine Value 〈401〉: NMT 3

Fats and Fixed Oils, Saponification Value 〈401〉: 150–165

5 ADDITIONAL REQUIREMENTS

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

Labeling: Label it to indicate the name and quantity of any added antioxidant.