Isopropyl Isostearate

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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INS: Isooctadecanoic acid, 1-methylethyl ester contains mainly isomers of isopropyl branched stearates. 

C₂₁H₄₂O₂ 326.56 

Isooctadecanoic acid, 1-methylethyl ester CAS RN®: 68171-33-5. 

1 DEFINITION 

Isopropyl Isostearate is obtained by esterification of isostearic acid, which is a mixture mainly of saturated branched 18 carbon-chain (C18) fatty acids and linear hexadecanoic (C16:0) and octadecanoic acids (C18:0), with isopropyl alcohol. 

2 IDENTIFICATION 

Change to read: 

Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197A or 197F. Disregard a weak absorption band at about 1780 cm^–1. 

It meets the requirements of the test for Content of Isopropyl Fatty Esters. 

3 ASSAY 

Content of Isopropyl Fatty Esters 

System suitability solution: 5.0 mg/mL of USP Isopropyl Palmitate RS and 0.5 mg/mL of USP Isopropyl Myristate RS in n-hexane Reference solution: 2.0 mg/mL of isopropyl stearate in n-hexane 

Sample solution: 5.0 mg/mL of Isopropyl Isostearate in n-hexane 

Chromatographic system 

(See Chromatography 〈621〉, System Suitability.) 

Mode: GC 

Detector: Flame ionization 

Column: 0.32-mm × 15-m fused silica; coated with a 1.0-µm layer of stationary phase G27 

Temperatures 

Injection port: 240° 

Detector: 280° 

Column: See Table 1. 

Table 1 

Carrier gas: Helium 

Flow rate: 1.5 mL/min 

Injection volume: 2.0 µL 

Injection type: Split injection, split ratio, 10:1 

Run time: About 35 min 

System suitability 

Samples: System suitability solution and Reference solution 

[Note—The relative retention times for isopropyl myristate, isopropyl palmitate, and isopropyl stearate are 0.8, 1.0, and 1.3, respectively.] Suitability requirements 

Resolution: NLT 6.0 between the isopropyl myristate and isopropyl palmitate peaks, System suitability solution 

Tailing factor: NMT 2 for the isopropyl palmitate peak, System suitability solution 

Relative standard deviation: NMT 2.0%, System suitability solution 

Analysis 

Samples: System suitability solution, Reference solution, and Sample solution 

Identify the isopropyl fatty ester peaks in the chromatogram of the Sample solution by comparing the retention times of these peaks with those obtained in the chromatograms of the System suitability solution and Reference solution, and measure the peak areas for all of the fatty acid ester peaks in the chromatogram obtained from the Sample solution. 

Calculate the percentage of each fatty acid ester component in the portion of Isopropyl Isostearate: 

Result = (r_U/r_T) × 100 

r_U = peak area for each individual fatty acid ester component 

r_T = sum of the peak areas, excluding the solvent peak, from the Sample solution 

Acceptance criteria 

Sum of the contents of the isopropyl fatty esters eluting between isopropyl palmitate and isopropyl stearate (excluding isopropyl palmitate and isopropyl stearate): NLT 65.0% 

Sum of the contents of isopropyl myristate, isopropyl palmitate, and isopropyl stearate: NMT 11.0% 

4 IMPURITIES 

Residue on Ignition 〈281〉: NMT 0.1% 

5 SPECIFIC TESTS 

Fats and Fixed Oils 〈401〉, Procedures, Acid Value: NMT 1.0, determined on 20.0 g 

Fats and Fixed Oils 〈401〉, Procedures, Hydroxyl Value: NMT 5.0 

Fats and Fixed Oils 〈401〉, Procedures, Iodine Value: NMT 3.0, determined on 3.0 g 

Fats and Fixed Oils 〈401〉, Procedures, Peroxide Value: NMT 5.0 

Fats and Fixed Oils 〈401〉, Procedures, Saponification Value: 165–180, determined on 2.0 g 

Water Determination 〈921〉, Method I: NMT 0.1%, determined on 5.0 g1 

6 ADDITIONAL REQUIREMENTS 

Packaging and Storage: Preserve in tight containers. Store at room temperature. 

Change to read: 

USP Reference Standards 〈11〉 

 USP Isopropyl Isostearate RS 

USP Isopropyl Myristate RS 

USP Isopropyl Palmitate RS 

¹ Hydranal composite 5 is suitable.