Polyethylene Glycol 40 Castor Oil

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

Polyethylene Glycol 40 Castor Oil contains mainly the triricinoleate ester of ethoxylated Glycerol with smaller amounts of polyethylene glycol ricinoleate and the corresponding free glycols. It results from the reaction of castor oil with 40 mol of ethylene oxide.

2 IDENTIFICATION

A. Test for Presence of Constituting Fatty Acids

Sample: 0.1 g

Analysis: Dissolve the Sample in 10 mL of potassium hydroxide TS, alcoholic; boil for 3 min and evaporate to dryness. Mix the residue with 5mL of water.

Acceptance criteria: The residue dissolves, yielding a clear solution. Add a few drops of glacial acetic acid. A white precipitate is formed.

B. Identity by Fatty Acid Composition

Diluent: n-Heptane

Standard solution 1: 0.2 mg/mL of each of USP Methyl Palmitate RS, USP Methyl Stearate RS, USP Methyl Oleate RS, USP Methyl Linoleate RS, methyl cis-11-eicosenoate, and USP Methyl Ricinoleate RS in Diluent

Standard solution 2: 4 mg/mL each of USP Methyl Stearate RS and USP Methyl Ricinoleate RS in Diluent

Sample solution: Transfer 140 mg of Polyethylene Glycol 40 Castor Oil to a 10-mL screw cap test tube, add 3.0 mL of Diluent, and mix well.

Add 0.5 mL of 0.5 M sodium methoxide in methanol¹ and mix with the sample. Allow the reaction to proceed at room temperature for 2 h.

After 2 h, add 5 mL of water and mix. Centrifuge the test tube at 1000 × g for 15 min until a clear upper layer forms. Remove the lower layer.

Place an aliquot of the organic layer (the upper layer) into an autosampler vial.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: GC

Detector: Flame ionization

Column: 0.25-mm × 15-cm fused silica capillary; bonded with a 0.25-μm layer of phase G7

Temperatures

Injection port: 240°

Detector: 250°

Column: See Table 1.

Table 1

Column mode: See Table 2 for the pressure program.

Table 2

Carrier gas: Hydrogen

Injection volume: 0.5 μL

Injection type: Split, split ratio 60:1

Liner: Single taper, low-pressure drop liner with deactivated wool

Run time: 45 min

System suitability

Sample: Standard solution 1

[Note—See Table 3 for relative retention times.]

Table 3

Suitability requirements

Resolution: NLT 1.5 between the methyl stearate and methyl oleate peaks

Relative standard deviation: NMT 2.0% for the peak area ratio of methyl ricinoleate to methyl linoleate

Analysis

Samples: Standard solution 2 and Sample solution

The peak of methyl cis-11-octadecenoate, which is an isomer of methyl oleate, can be resolved from the methyl oleate peak with a resolution of about 1 and a relative retention time of 1.01 with respect to methyl oleate.

Calculate the relative response factor, F, for methyl ricinoleate:

F = (r_S/r_R) × (C_R/C_S)

r_S = peak area of methyl stearate from Standard solution 2

r_R = peak area of methyl ricinoleate from Standard solution 2

C_R = concentration of USP Methyl Ricinoleate RS in Standard solution 2 (mg/mL)

C_S = concentration of USP Methyl Stearate RS in Standard solution 2 (mg/mL)

Correct the peak area of methyl ricinoleate in the Sample solution by multiplying by F.

Calculate the percentage of each fatty acid component in the portion of Polyethylene Glycol 40 Castor Oil taken:

Result = (r_U/r_T) × 100

r_U = peak area of each individual fatty acid methyl ester, except for the uncorrected peak area of methyl ricinoleate (or the corrected peak area of methyl ricinoleate), from the Sample solution

r_T = sum of all the peak areas, excluding the solvent and methyl ricinoleate peaks and including the corrected peak area of methyl ricinoleate, from the Sample solution

Acceptance criteria: Polyethylene Glycol 40 Castor Oil exhibits the composition profile of fatty acids shown in Table 4.

Table 4

3 IMPURITIES

Residue on Ignition 〈281〉: NMT 0.3%

Ethylene Oxide and Dioxane 〈228〉, Method I

Acceptance criteria

For ethylene oxide: NMT 1 μg/g

For dioxane: NMT 10 μg/g

Ethylene Glycol, Diethylene Glycol, and Triethylene Glycol in Ethoxylated Substances 〈469〉

Acceptance criteria

For ethylene glycol: NMT 620 μg/g

For diethylene glycol: NMT 1000 μg/g

4 SPECIFIC TESTS

Specific Gravity 〈841〉: 1.05–1.06

Viscosity—Capillary Methods 〈911〉: 600–850 mPa · s at 25°, using a capillary viscometer

Fats and Fixed Oils 〈401〉, Procedures, Acid Value: NMT 1.0

Fats and Fixed Oils 〈401〉, Procedures, Hydroxyl Value: 60–75

Fats and Fixed Oils 〈401〉, Procedures, Iodine Value: 29–33

Fats and Fixed Oils 〈401〉, Procedures, Saponification Value: 57–70

Water Determination 〈921〉, Method I, Method Ic: NMT 3.0%

5 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers, protected from light and moisture. Store at room temperature and avoid exposure to excessive heat.

USP Reference Standards 〈11〉

USP Methyl Linoleate RS

USP Methyl Oleate RS

USP Methyl Palmitate RS

USP Methyl Ricinoleate RS

USP Methyl Stearate RS (NF 1-Dec-2024)