Glyceryl Mono and Dicaprylate

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 

Glyceryl Mono and Dicaprylate is a mixture of glyceryl monoester and diesters, mainly mono- and di-O-octanoylglycerol, containing variable quantities of triesters of fatty acids composed predominately of caprylic acid. The requirements for monoester, diester, and triester content are: Monoesters: 40.0%–75.0%; Diesters: 20.0%–50.0%; and Triesters: NMT 15.0%. 

2 IDENTIFICATION 

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2.1 A. Fatty Acid Composition 

Boron triuoride methanol solution: 140 mg/mL of boron triuoride in methanol 

Saturated sodium chloride solution: Mix 1 part sodium chloride with 2 parts water, shake from time to time, and allow to stand. Before use, decant the solution from any undissolved substance and lter, if necessary. 

Standard solution 1: 1.0 mg/mL of USP Methyl Caproate RS, 1.0 mg/mL of USP Methyl Caprylate RS, and 2.0 mg/mL of USP Methyl Caprate RS in n-heptane 

Standard solution 2: 0.1 mg/mL of USP Methyl Caproate RS, 0.1 mg/mL of USP Methyl Caprylate RS, and 0.2 mg/mL of USP Methyl Caprate RS in n-heptane, diluted from Standard solution 1 

Standard solution 3: Prepare an ester mixture either by mixing a commercially available ester mixture with methyl caprylate and methyl caprate or by using USP Methyl Caproate RS, USP Methyl Caprylate RS, USP Methyl Caprate RS, USP Methyl Laurate RS, and USP Methyl Myristate RS. (ERR 1-May-2020) Dissolve a quantity of the prepared ester mixture containing methyl caproate, methyl caprylate, methyl caprate, methyl laurate, and methyl myristate in n-heptane to make a solution of about 9.0 mg/mL for methyl caprylate, 1.0 mg/mL for methyl caprate, and 0.05–0.1 mg/mL for each of the other methyl esters. 

Sample solution: Transfer 100 mg of Glyceryl Mono and Dicaprylate to a 25-mL conical ask tted with a suitable water-cooled reux condenser and a magnetic stir bar. Add 2 mL of a 20-mg/mL solution of sodium hydroxide in methanol, mix, and reux for about 30 min. Add 2 mL of Boron triuoride methanol solution through the condenser, and reux for about 30 min. Add 4 mL of n-heptane through the condenser and reux for 5 min. Cool, remove the condenser, add about 10 mL of Saturated sodium chloride solution, shake, add a quantity of Saturated sodium chloride solution to bring the upper layer up to the neck of the ask, and allow the layers to separate. Collect 2 mL of the n-heptane layer (upper layer), wash with three quantities each of 2 mL of water, and dry the n-heptane phase over anhydrous sodium sulfate. 

Chromatographic system 

(See Chromatography 〈621〉, System Suitability.) 

Mode: GC 

Detector: Flame ionization 

Column: 0.53-mm × 30-m capillary; bonded with a 1.0-µm layer of phase G16 

Temperatures 

Injection port: 250° 

Detector: 250° 

Column: See Table 1. 

Table 1 

Carrier gas: Helium Flow rate: 10 mL/min Injection volume: 2 µL 

Injection type: Split injection; split ratio, 4:1 

System suitability 

Samples: Standard solution 1 and Standard solution 2[Note—The relative retention times for methyl caproate, methyl caprylate, and methyl caprate are about 0.7, 1.0, and 1.3, respectively.] 

Suitability requirements 

Resolution: NLT 4.0 between the methyl caprylate and methyl caprate peaks, Standard solution 1 

Signal-to-noise ratio: NLT 10 for the methyl caproate peak, Standard solution 2 

Analysis 

Samples: Standard solution 3 and Sample solution 

Measure the peak areas for the methyl esters of the fatty acids. Disregard any peaks with an area less than 0.05% of the total area and any peak due to the solvent. [Note—The relative retention times for several methyl esters are summarized in Table 2.] 

Table 2 

Take the main component in Standard solution 3 as a reference component and calculate the calibration factor, F_FA, for each fatty acid methyl ester: 

F_FA = (F_MC × P_FA1 × A_MC)/(P_MC × A_FA1) 

F_MC = factor for the main component, 1 

P_FA1 = percentage by weight of the fatty acid methyl ester in Standard solution 3 

A_MC = peak area of the main component from Standard solution 3  

P_MC = percentage by weight of the main component in Standard solution 3 

A_FA1 = peak area of the fatty acid methyl ester from Standard solution 3 

Calculate the percentage of the fatty acid methyl ester by weight in the portion of Glyceryl Mono and Dicaprylate taken: 

Result = [(A_FA2 × F_FA)/A_T] × 100 

A_FA2 = peak area of the fatty acid methyl ester from the Sample solution 

A_T = sum of the peak areas of the fatty acid methyl esters from the Sample solution 

Acceptance criteria: Glyceryl Mono and Dicaprylate exhibits the composition prole of fatty acids shown in Table 3. Table 3 

2.2 B. Glyceride Content:

It meets the requirements of the test for Content of Monoglycerides, Diglycerides, and Triglycerides in the Assay.

2.3 C. Fats and Fixed Oils 〈401〉, Procedures, Saponification Value: 266–300 

3 ASSAY 

3.1 Content of Monoglycerides, Diglycerides, and Triglycerides 

System suitability solution: 20 mg/mL each of 1-monooctanoyl-rac-glycerol and 1-monodecanoyl-rac-glycerol in tetrahydrofuran Standard solution: 50 mg/mL of USP Glyceryl Monocaprylate RS in tetrahydrofuran 

Sample solution: 50 mg/mL of Glyceryl Mono and Dicaprylate in tetrahydrofuran 

Chromatographic system 

(See Chromatography 〈621〉, System Suitability.) 

Mode: GC 

Detector: Flame ionization 

Column: 0.32-mm × 10-m; bonded with a 0.1-µm layer of phase G27 

Temperatures 

Injection port: 350° 

Detector: 370° 

Column: See Table 4. 

Table 4 

Carrier gas: Helium 

Flow rate: 2.3 mL/min 

Injection volume: 1 µL 

Injection type: Split injection; split ratio, 50:1 

System suitability 

Samples: System suitability solution and Standard solution[Note—The typical relative retention times for monoglycerides, diglycerides, and triglycerides are 1.0–1.2, 1.5–1.9, and 2.0–2.3, respectively, Standard solution.] 

Suitability requirements 

Resolution: NLT 5.0 between the 1-monooctanoyl-rac-glycerol and 1-monodecanoyl-rac-glycerol peaks, System suitability solution Analysis 

Samples: Standard solution and Sample solution 

Based on the chromatogram from the Standard solution, identify the peaks due to monoglycerides, diglycerides, and triglycerides in the 

Sample solution. 

For the calculation of the contents of monoglycerides, diglycerides, and triglycerides, disregard the peaks with retention times less than those of the monoglycerides, which are due to impurities of the solvent and to the free fatty acids. 

Calculate the percentage content of free fatty acids (C_A): 

C_A = [(I_A × F × M_r1)/M_r2] × 100 

I_A = acid value for Glyceryl Mono and Dicaprylate, determined from the test for Acid Value 

F = conversion factor, 10−3 g/mg 

M_r1 = molecular weight of caprylic acid, 144.21 g/mol 

M_r2 = molecular weight of potassium hydroxide, 56.11 g/mol 

Calculate the percentage of monoglycerides, diglycerides, or triglycerides in the portion of Glyceryl Mono and Dicaprylate taken: 

Result = (r_U/r_T) × [(100 − C_A − C_W − C_G)/100] × 100 

r_U = peak response of the monoglycerides, diglycerides, or triglycerides from the Sample solution 

r_T = sum of all the glyceride peak responses from the Sample solution 

C_A = percentage of free fatty acids, determined above 

C_W = percentage of water, determined from the test for Water Determination 

C_G = percentage of free Glycerin, determined from the test for Limit of Free Glycerol 

Acceptance criteria 

Monoesters: 40.0%–75.0% 

Diesters: 20.0%–50.0% 

Triesters: NMT 15.0% 

4 IMPURITIES 

4.1 Total Ash 

Sample: 1.0 g 

Analysis: Heat a silica or platinum crucible to redness for 30 min, allow to cool in a desiccator, and weigh. Evenly distribute the Sample in the crucible. Dry at 100°–105° for 1 h and ignite to constant weight in a mue furnace at 600 ± 25°, allowing the crucible to cool in a desiccator after each ignition. Flames should not be produced at any time during the procedure. If after prolonged ignition the ash still contains black particles, take up with hot water, pass through an ashless lter paper, and ignite the residue and the lter paper. Combine the ltrate with the ash, carefully evaporate to dryness, and ignite to constant mass. 

Acceptance criteria: NMT 0.5% 

4.2 Limit of Free Glycerol 

Sample: 1.2 g 

Periodic acetic acid solution: Dissolve 0.446 g of sodium periodate in 2.5 mL of a 25% (v/v) solution of sulfuric acid, and dilute with glacial acetic acid to 100.0 mL. 

Potassium iodide solution: 75 mg/mL of potassium iodide 

Blank: 25 mL of methylene chloride 

Titrimetric system 

(See Titrimetry 〈541〉.) 

Mode: Residual titration 

Titrant: 0.1 M sodium thiosulfate VS 

Endpoint detection: Visual 

Analysis: Dissolve the Sample in 25 mL of methylene chloride. Heat to about 50° and allow to cool. Add 100 mL of water. Shake and add 25 mL of Periodic acetic acid solution. Shake again and allow to stand for 30 min. Add 40 mL of Potassium iodide solution, and allow to stand for 1 min. Add 1 mL of starch TS and titrate the liberated iodine with Titrant until the aqueous phase becomes colorless. Perform a blank determination. 

Calculate the percentage of free Glycerol in the portion of Glyceryl Mono and Dicaprylate taken: 

Result = {[(V_B − V_S) × N × E × F]/W} × 100 

V_B = volume of Titrant consumed in the Blank titration (mL) 

V_S = volume of Titrant consumed in the Sample titration (mL) 

N = actual normality of the Titrant (mEq/mL) 

E = equivalent factor for glycerol, 23 mg/mEq 

F = conversion factor, 10−3 g/mg 

W = weight of Glyceryl Mono and Dicaprylate taken for the titration (g) 

Acceptance criteria: NMT 3.0% 

5 SPECIFIC TESTS 

Fats and Fixed Oils 〈401〉, Procedures, Acid Value: NMT 3.0 

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

Water Determination 〈921〉, Method I, Method Ia: NMT 1.0% 

6 ADDITIONAL REQUIREMENTS 

6.1 Packaging and Storage:

Preserve in tight containers, and store at room temperature. Protect from moisture. 

6.2 USP Reference Standards 〈11〉 

USP Glyceryl Monocaprylate RS 

USP Methyl Caprate RS 

USP Methyl Caproate RS 

USP Methyl Caprylate RS 

USP Methyl Laurate RS 

USP Methyl Myristate RS (NF 1-May-2020)