Isostearyl 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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1 DEFINITION 

Isostearyl Isostearate is obtained by esterication of isostearic acid which is a mixture mainly of saturated branched 18 carbon-chain (C18) fatty acids, linear hexadecanoic (C16:0) and octadecanoic acids (C18:0), with isostearyl alcohol. It contains NLT 85.0% of isostearyl isostearate. 

2 IDENTIFICATION 

2.1 A. Ester 

Analysis 1: Proceed as directed in Fats and Fixed Oils 〈401〉, Procedures, Saponication Value. 

Sample: 3 g 

Analysis: Proceed as directed in the chapter. Heat under reux for 1 h. 

Acceptance criteria: 90–110  

Analysis 2: Proceed as directed in Fats and Fixed Oils 〈401〉, Procedures, Acid Value. 

Sample: Sample amount (see Fats and Fixed Oils 〈401〉, Table 1) 

Acceptance criteria: NMT 6.0 

2.2 B. Chromatographic Identity 

Analysis: Proceed as directed in the Assay. 

Acceptance criteria: The retention time of the major peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay. 

3 ASSAY 

3.1 Procedure 

Mobile phase: Tetrahydrofuran 

Reference solution: 2 mg/mL of isostearic acid in Mobile phase 

Standard solution: 40 mg/mL of USP Isostearyl Isostearate RS in Mobile phase 

Sample solution: 40 mg/mL of Isostearyl Isostearate in Mobile phase 

Chromatographic system 

(See Chromatography 〈621〉, System Suitability.) 

Mode: LC 

Detector: Differential refractive index 

Column: Two 7.5-mm × 30-cm columns in tandem; 3-µm packing L21 

Temperatures 

Column: 35° 

Detector: 35° 

Flow rate: 1.0 mL/min 

Injection volume: 20 µL 

Run time: 30 min 

System suitability 

Samples: Reference solution and Standard solution 

[Note—The relative retention times for isostearyl isostearate, isostearic acid, and isostearyl alcohol are 1.00, 1.07, and 1.09, respectively.] Suitability requirements 

Resolution: NLT 1.3 between the isostearyl isostearate peak and the adjacent peak at the retention time 1.09 relative to isostearyl isostearate, Standard solution 

Relative standard deviation: NMT 2.0%, determined from the isostearyl isostearate peak, Standard solution 

Analysis 

Samples: Standard solution and Sample solution 

Calculate the percentage of isostearyl isostearate in the portion of Isostearyl Isostearate taken: 

Result = (r_u/r_s) × (C_s/C_u) × 100

r_u = peak response of isostearyl isostearate from the Sample solution 

r_s = peak response of isostearyl isostearate from the Standard solution 

C_s = concentration of USP Isostearyl Isostearate RS in the Standard solution 

C_u = concentration of Isostearyl Isostearate in the Sample solution 

Acceptance criteria: NLT 85.0% 

4 IMPURITIES 

Residue on Ignition 〈281〉: NMT 0.2% 

5 SPECIFIC TESTS 

5.1 Fats and Fixed Oils 〈401〉, Procedures, Hydroxyl Value 

Sample: 4 g 

Analysis: Proceed as directed in the chapter. A sand bath can be used. 

Acceptance criteria: NMT 25.0 

5.2 Fats and Fixed Oils 〈401〉, Procedures, Iodine Value 

Sample: 3 g 

Acceptance criteria: NMT 5.0 

5.3 Fats and Fixed Oils 〈401〉, Procedures, Peroxide Value 

Sample: 3 g 

Acceptance criteria: NMT 5.0 

5.4 Water Determination 〈921〉, Method I 

Sample: 3 g 

Acceptance criteria: NMT 0.5% 

5.5 Refractive Index 〈831〉: 1.454–1.464 at 25° 

6 ADDITIONAL REQUIREMENTS 

6.1 Packaging and Storage:

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

6.2 USP Reference Standards 〈11〉 

USP Isostearyl Isostearate RS