Polyoxyl 35 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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Polyethylene glycol 35 castor oil;

Polyoxyethylene 35 castor oil

CAS RN®: 61791-12-6.

1 DEFINITION

Polyoxyl 35 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 glycerol ricinoleate with 35 mol of ethylene oxide.

2 IDENTIFICATION

Change to read:

A. Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197F  (CN 1-May-2020)

B. 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.

Change to read:

C. Identity by Fatty Acid Composition

Diluent: n-Heptane

Standard solution 1: 0.2 mg/mL each of methyl palmitate, methyl stearate, methyl oleate, methyl linoleate, methyl cis-11-eicosenoate, and methyl ricinoleate, from 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 methyl stearate and methyl ricinoleate from USP Methyl Stearate RS and USP Methyl Ricinoleate RS in Diluent

Sample solution: Transfer 140 mg of Polyoxyl 35 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 methanol,¹ 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 10–15 min until a clear upper layer forms. Separate the organic layer (the upper layer), and remove the lower layer. Place an aliquot of the organic layer into an autosampler vial.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: GC

Detector: Flame ionization

Column: 0.25-mm × 15-m 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

^a If considerable discrimination of late eluting compounds is observed, the hold time can be adjusted from 9 to 0 min. Thus the total time should be 17.2 min. Then the next step of the hold time should be 28 min.

Carrier gas: Hydrogen

Injection volume: 0.5 μL

Injection type: 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 methyl stearate and methyl oleate peaks

Relative standard deviation: NMT 2.0% for the peak area ratio of methyl ricinoleate to methyl linoleate (ERR 1-May-2020)

Analysis

Samples: Standard solution 1, 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 Polyoxyl 35 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: Polyoxyl 35 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

Ethylene oxide: NMT 1 μg/g

Dioxane: NMT 10 μg/g

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

Acceptance criteria

Ethylene glycol: NMT 620 μg/g

Sum of diethylene glycol and ethylene glycol: NMT 2500 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 2.0

Fats and Fixed Oils 〈401〉, Procedures, Hydroxyl Value: 65–80

Fats and Fixed Oils 〈401〉, Procedures, Iodine Value: 25–35

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

Water Determination 〈921〉, Method I: 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

USP Polyoxyl 35 Castor Oil RS

¹ 0.5 M sodium methoxide in methanol is available from Sigma-Aldrich (www.sigmaaldrich.com), product #403067. Any other equivalent reagent can be used as well.