Zinc Undecylenate

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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C₂₂H₃₈O₄Zn 431.92

10-Undecenoic acid, zinc(2+) salt;

Zinc 10-undecenoate CAS RN®: 557-08-4; UNII: 388VZ25DUR.

1 DEFINITION

Zinc Undecylenate contains NLT 98.0% and NMT 102.0% of zinc undecylenate (C₂₂H₃₈O₄Zn), calculated on the dried basis.

2 IDENTIFICATION

A. Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197A

B. The retention time of the Undecylenic Acid peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay.

C.

Sample: 100 mg of Zinc Undecylenate

Analysis: Dissolve the Sample in a mixture of 10 mL of water and 1 mL of ammonium hydroxide, and add a few drops of sodium sulfide TS.

Acceptance criteria: A white, occulent precipitate of zinc sulfide is formed.

3 ASSAY

Change to read:

Procedure

Solution A: 0.15 N hydrochloric acid in water prepared as follows. Transfer 150 mL of 0.5 N (ERR 1-Dec-2022) hydrochloric acid to a 500-mL volumetric flask, dilute with water to volume, and mix well.

Standard solution: 0.5 mg/mL of USP Undecylenic Acid RS in n-heptane, prepared as follows. Accurately weigh and transfer 25 mg of USP Undecylenic Acid RS to a suitable flask, add 20 mL of Solution A, and heat until the sample is liquified and transparent with two immiscible layers. Cool, upon which turbidity may be observed. Add 50 mL of n-heptane to the flask, and mix well. Transfer the n-heptane layer to a suitable container, and dry over anhydrous sodium sulfate. Centrifuge to clarify the mixture, and use the clear supernatant.

Sample solution: Nominally 0.5 mg/mL of undecylenic acid in n-heptane, prepared as follows. Accurately weigh and transfer 29.3 mg of Zinc Undecylenate, equivalent to 25 mg of undecylenic acid, to a suitable flask. Follow the preparation steps described in the Standard solution.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: GC

Detector: Flame ionization

Column: 0.25-mm × 30-m fused-silica capillary; coated with a 0.25-μm film of phase G35

Temperatures

Injection port: 280°

Detector: 350°

Column: See Table 1.

Table 1

Carrier gas: Helium

Flow rate: 0.7 mL/min

Injection volume: 1 μL

Injection type: Split, split ratio 25:1

System suitability

Sample: Standard solution

Suitability requirements

Tailing factor: NMT 2.0

Relative standard deviation: NMT 1.0%

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of zinc undecylenate (C₂₂H₃₈O₄Zn) in the portion of Zinc Undecylenate taken:

Result = (r_U/r_S) × (C_S/C_U) × [M_r1/(2 × M_r2)] × 100

r_U = peak response of undecylenic acid from the Sample solution

r_S = peak response of undecylenic acid from the Standard solution

C_S = concentration of USP Undecylenic Acid RS in the Standard solution (mg/mL)

C_U = concentration of Zinc Undecylenate in the Sample solution (mg/mL)

M_r1 = molecular weight of zinc undecylenate, 431.92

M_r2 = molecular weight of undecylenic acid, 184.28

Acceptance criteria: 98.0%–102.0% on the dried basis

4 IMPURITIES

4.1 Alkalies and Alkaline Earths

Sample solution: Boil 1.50 g of Zinc Undecylenate with a mixture of 50 mL of water and 10 mL of hydrochloric acid, filter while hot, and wash the separated acid portion with 50 mL of hot water. Render the combined filtrate and washings alkaline with 6 N ammonium hydroxide. Add ammonium sulfide TS to precipitate the zinc completely, dilute with water to 200 mL, and filter. Use the clear filtrate.

Analysis: To 100 mL of the Sample solution, add 0.5 mL of sulfuric acid, evaporate to dryness, and ignite over a low flame to constant weight.

Acceptance criteria: The weight of the residue is NMT 7.5 mg (1.0%).

4.2 Limit of Free Undecylenic Acid

Sensitivity solution: 0.005 mg/mL of USP Undecylenic Acid RS in n-heptane

Standard solution: 0.01 mg/mL of USP Undecylenic Acid RS in n-heptane

Sample solution: 10 mg/mL of Zinc Undecylenate in n-heptane prepared as follows. Accurately weigh and transfer 100 mg of Zinc Undecylenate into a suitable container, add 10 mL of n-heptane, and mix for 2 h by magnetic stirring. Centrifuge to clarify the mixture, and use the clear supernatant.

Chromatographic system: Proceed as directed in the Assay except for the Injection type.

Injection type: Split, split ratio 10:1

System suitability

Samples: Sensitivity solution and Standard solution

Suitability requirements

Relative standard deviation: NMT 5.0%, Standard solution

Signal-to-noise ratio: NLT 10, Sensitivity solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of undecylenic acid (C₁₀H₂₀O₂) in the portion of Zinc Undecylenate taken:

Result = (r_U/r_S) × (C_S/C_U) × 100

r_U = peak response of undecylenic acid from the Sample solution

r_S = peak response of undecylenic acid from the Standard solution

C_S = concentration of USP Undecylenic Acid RS in the Standard solution (mg/mL)

C_U = concentration of Zinc Undecylenate in the Sample solution (mg/mL)

Acceptance criteria: NMT 0.1%

5 SPECIFIC TESTS

Loss on Drying 〈731〉

Analysis: Dry at 105° for 2 h.

Acceptance criteria: NMT 1.25%

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers.

USP Reference Standards 〈11〉

USP Zinc Undecylenate RS

USP Undecylenic Acid RS