Cetyl Esters Wax

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

DOWNLOAD PDF HERE

1 DEFINITION

Cetyl Esters Wax is a mixture consisting primarily of esters of saturated fatty alcohols (C₁₂ to C₂₀) and saturated fatty acids (C₁₂ to C₂₀). It contains NLT 90.0% of total saturated fatty esters and NLT 10.0% of fatty esters with carbon-chain length of carbon number 32 that consist chiefly of cetyl palmitate.

2 IDENTIFICATION

A. Chromatographic Identity

Analysis: Proceed as directed in the test for Total Fatty Esters and Cetyl Palmitate in the Assay.

Acceptance criteria: The retention times of the four major fatty ester peaks (fatty esters with carbon-chain length of carbon number 28, fatty esters with carbon-chain length of carbon number 30, fatty esters with carbon-chain length of carbon number 32, and fatty esters with carbon-chain length of carbon number 34) of the Sample solution correspond to those of Reference solution D.

B. Fats and Fixed Oils 〈401〉, Procedures, Saponification Value: 109–120

3 ASSAY

Total Fatty Esters and Cetyl Palmitate

Reference solution A: 1 mg/mL of USP Lauryl Alcohol RS, 1 mg/mL of USP Myristyl Alcohol RS, 1 mg/mL of USP Cetyl Alcohol RS, and 1 mg/mL of USP Stearyl Alcohol RS in n-hexane

Reference solution B: 1 mg/mL of USP Palmitic Acid RS in n-hexane

Reference solution C: 1 mg/mL of USP Cetyl Palmitate RS in n-hexane

Reference solution D: 1 mg/mL of USP Cetyl Esters Wax RS in n-hexane

Sample solution: 1 mg/mL of Cetyl Esters Wax in n-hexane

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: GC

Detector: Flame ionization

Column: 0.53-mm × 10-m fused-silica capillary; 2.65-µm layer of phase G2

Temperatures

Injection port: 350°

Detector: 350°

Column: See Table 1.

Carrier gas: Helium

Flow rate: 6.5 mL/min

Injection volume: 1 µL

Injection type: Split ratio, 10:1

Run time: 25 min

System suitability

Samples: Reference solution A, Reference solution B, Reference solution C, and Reference solution D

[Note—For relative retention times, see Table 2.]

Suitability requirements:

Resolution: NLT 2.0 between fatty esters with carbon-chain length of carbon number 32 and fatty esters with carbon-chain length of carbon number 34, Reference solution D

Analysis

Samples: Reference solution A, Reference solution B, Reference solution C, Reference solution D, and Sample solution

Identify fatty alcohols, fatty acids, and fatty esters based on the chromatograms from Reference solution A, Reference solution B, Reference solution C, and Reference solution D, and also according to Table 2.

Calculate the percentage of each individual group of fatty esters (fatty esters with carbon-chain length of carbon number 26, fatty esters with carbon-chain length of carbon number 28, fatty esters with carbon-chain length of carbon number 30, fatty esters with carbon-chain length of carbon number 32, fatty esters with carbon-chain length of carbon number 34, or fatty esters with carbon-chain length of carbon number 36) (P_FE) in the portion of Cetyl Esters Wax taken:

Result (P_FE) = (r_U / r_T) × 100

r_U = peak area of each individual group of fatty esters

r_T = sum of the total peak areas from the Sample solution, except for the peak areas from solvent

Calculate the percentage of total saturated fatty esters in the portion of Cetyl Esters Wax taken:

Result = ΣP_FE

Acceptance criteria

Total saturated fatty esters: NLT 90.0%

Fatty esters with carbon-chain length of carbon number 32 that consist chiefly of cetyl palmitate: NLT 10.0%

4 IMPURITIES

Limit of Total Free Fatty Alcohols and Free Fatty Acids

Reference solution A, Reference solution B, Reference solution D, Sample solution, Chromatographic system, and System suitability: Proceed as directed in the test for Total Fatty Esters and Cetyl Palmitate.

Analysis

Samples: Reference solution A, Reference solution B, Reference solution D, and Sample solution

Identify fatty alcohols, fatty acids, and fatty esters based on the chromatograms from Reference solution A, Reference solution B, and Reference solution D, and also according to Table 2.

Calculate the percentage of each individual fatty alcohol (lauryl alcohol, myristyl alcohol, cetyl alcohol, or stearyl alcohol) or fatty acid (lauric acid, myristic acid, palmitic acid, or stearic acid) (P_FA) in the portion of Cetyl Esters Wax taken:

Result (P_FE) = (r_U / r_T) × 100

r_U = peak area of each individual fatty alcohol or fatty acid from the Sample solution

r_T= sum of the total peak areas from the Sample solution, except for the peak areas from solvent

Calculate the percentage of total fatty alcohols and fatty acids in the portion of Cetyl Esters Wax taken:

Result = ΣP_FE

Acceptance criteria

Total free fatty alcohols and free fatty acids: NMT 10.0%

5 SPECIFIC TESTS

Melting Range or Temperature 〈741〉, Procedures, Procedure for Class II: 43°–47°

Fats and Fixed Oils 〈401〉, Procedures, Acid Value: NMT 5

Fats and Fixed Oils 〈401〉, Procedures, Iodine Value: NMT 1

Paraffin and Free Acids

Sample: 1 g

Analysis: Dissolve the Sample in 50 mL of boiling alcohol.

Acceptance criteria: The Sample dissolves completely, and the resulting solution is neutral or acidic to moistened litmus paper.

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers, in a dry place, and prevent exposure to excessive heat.

Labeling: Label to indicate the percentages of fatty esters with carbon-chain length of carbon number 26, fatty esters with carbon-chain length of carbon number 28, fatty esters with carbon-chain length of carbon number 30, fatty esters with carbon-chain length of carbon number 32, fatty esters with carbon-chain length of carbon number 34, and fatty esters with carbon-chain length of carbon number 36.

USP Reference Standards 〈11〉

USP Cetyl Alcohol RS

USP Cetyl Esters Wax RS

USP Cetyl Palmitate RS

USP Lauryl Alcohol RS

USP Myristyl Alcohol RS

USP Palmitic Acid RS

USP Stearyl Alcohol RS