Monoglyceride Citrate

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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Citric acid ester of glyceryl monooleate

CAS RN^®: 36291-32-4.

1 DEFINITION

Monoglyceride Citrate is a mixture of glyceryl monooleate and its citric acid monoester, manufactured by the reaction of glyceryl monooleate with citric acid under controlled conditions. It contains NLT 14.0% and NMT 17.0% of total citric acid, calculated on the anhydrous basis.

2 IDENTIFICATION

2.1 A.

Sample: 1 g

Analysis: Reflux the Sample with 15 mL of 0.5 N potassium hydroxide solution in dehydrated alcohol for 1 h. Add 15 mL of water, and acidify with diluted hydrochloric acid (about 6 mL). Dissolve any oil drops or solid produced in 5 mL of hexane. Remove the hexane layer, extract again with 5 mL of hexane, and again remove the hexane layer.

[NOTE-Keep the resulting aqueous layer for Identification tests B and C.]

Acceptance criteria: Oil drops or a white to yellowish-white solid are produced that are soluble in 5 mL of hexane.

2.2 B. IDENTIFICATION TESTS-GENERAL, Citrate (191)

Sample: 1 mL of the aqueous layer resulting from Identification test A

Analysis: Evaporate the Sample in a porcelain dish.

Acceptance criteria: The residue meets the requirements.

2.3 C.

Sample: 5 mL of the aqueous layer resulting from Identification test A

Analysis: Transfer the Sample to a test tube. Add excess calcium hydroxide as a powder, place in boiling water for 5 min, shaking several times, cool, and filter. Transfer one drop of the filtrate into a test tube, and add about 50 mg of potassium hydrogen sulfate. On top of the test tube, place a filter paper moistened with a reagent for acrolein consisting of a mixture of 5% nitroprusside solution in water and 20% piperidine solution in water (1:1). Heat the test tube.

Acceptance criteria: The filter paper turns blue (presence of Glycerin). The color changes to light red after addition of sodium hydroxide TS.

3 ASSAY

3.1 CONTENT OF CITRIC ACID

Standard solution: 0.23 mg/mL of USP Citric Acid RS

Sample solution: Transfer 150 mg of Monoglyceride Citrate into a saponification flask, add 50 mL of 4% potassium hydroxide solution in dehydrated alcohol, and reflux for 1 h. Acidify the reaction mixture with hydrochloric acid to a pH of 2.8-3.2, transfer into a 400-mL beaker, and evaporate to dryness on a steam bath. Quantitatively transfer the contents of the beaker into a separator, using NMT 50 mL of water, and extract with three 50-mL portions of petroleum ether, discarding the extracts. Transfer the water layer to a 100-mL volumetric flask, and dilute with water to volume.

Blank: Water

Instrumental conditions

Mode: UV-Vis

Analytical wavelength: 450 nm

Cell: 1 cm

Analysis

Samples: Standard solution, Sample solution, and Blank

Pipet 2.0 mL each of the Standard solution, Sample solution, and Blank into separate 40-ml graduated centrifuge tubes. Add 2 mL of a 1 in 2 sulfuric acid solution and 11 mL of water to each tube. Boil for 3 min, cool, and add 5 mL of bromine TS to each tube. Dilute to 20 mL, allow to stand for 10 min, and centrifuge. Transfer 4.0 mL of the supernatant from each tube into separate 19-x110-mm test tubes, add 1 mL of water, 0.5 mL of a 1 in 2 sulfuric acid solution, and 0.3 mL of 1 M potassium bromide, and shake. Add 0.3 mL of 1.5 N potassium permanganate, shake, and allow to stand for 2 min. Add 1 mL of a saturated solution of ferrous sulfate, shake, allow to stand for 2 min, and then dilute with water to 10 mL. Add 10.0 mL of n-hexane (previously washed with sulfuric acid, followed by a water wash, and then dried over anhydrous sodium sulfate), shake vigorously for 2 min, and centrifuge at low speed for 1 min. Transfer 5.0 mL of the hexane extract into a 20-x 145-mm tube containing 10.0 mL of 4% sodium sulfide solution, and briefly shake vigorously (three oscillations only). Centrifuge the mixture at low speed for 1 min. Immediately determine the absorbance of each aqueous layer from the Standard solution and Sample solution against the aqueous layer from the Blank.

Calculate the percentage of citric acid in the portion of Monoglyceride Citrate taken:

                 Result = (A_U/A_S) x (V x C_S/W) x 100

A_U = absorbance of the Sample solution

A_S = absorbance of the Standard solution

V = volume of the Sample solution (mL)

C_S = concentration of USP Citric Acid RS in the Standard solution (mg/mL)

W = weight of Monoglyceride Citrate taken to prepare the Sample solution (mg)

Acceptance criteria: 14.0%-17.0% on the anhydrous basis

4 IMPURITIES

RESIDUE ON IGNITION (281): NMT 0.3%, determined on 1 g

5 SPECIFIC TESTS

FATS AND FIXED OILS, Acid Value(401): 70-100

FATS AND FIXED OILS, Saponification Value(401): 260-265

WATER DETERMINATION, Method (921): NMT 0.2%

6 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in well-closed containers. No storage requirements specified.

USP REFERENCE STANDARDS (11)

USP Citric Acid RS