Equilin

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

Equilin contains NLT 97.0% and NMT 103.0% of equilin (C₁₈H₂₀O₂), calculated on the dried basis.

2 IDENTIFICATION

Change to read:

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

Change to read:

B. Spectroscopic Identification Tests 〈197〉, Ultraviolet-Visible Spectroscopy: 197U (CN 1-May-2020)

Sample solution: 50 μg/mL in alcohol

3 ASSAY

Procedure

Mobile phase: Acetonitrile and water (35:65)

Internal standard solution: 35 μg/mL of phenol in acetonitrile

Standard solution: 0.2 mg/mL of USP Equilin RS in Internal standard solution

Sample solution: 0.2 mg/mL of Equilin in Internal standard solution

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 280 nm

Column: 3.9-mm × 30-cm; packing L1

Flow rate: 2 mL/min

Injection volume: 20 μL

System suitability

Sample: Standard solution

[Note—The retention times for phenol and equilin are 3 and 14 min, respectively.]

Suitability requirements

Resolution: NLT 5 between equilin and phenol. Adjust the operating parameters such that the peak of the Standard solution is about 0.7 full-scale.

Relative standard deviation: NMT 2.0% for five replicate injections

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of equilin (C₁₈H₂₀O₂) in the portion of Equilin taken:

Result = (R_U/R_S) × (C_S/C_U) × 100

R_U = peak response ratio of equilin to the internal standard from the Sample solution

R_S = peak response ratio of equilin to the internal standard from the Standard solution

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

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

Acceptance criteria: 97.0%–103.0% on the dried basis

4 IMPURITIES

Residue on Ignition 〈281〉: NMT 0.5%

5 SPECIFIC TESTS

Optical Rotation, Specific Rotation 〈781S〉

Sample solution: 20 mg/mL, in dioxane

Acceptance criteria: +300° to +316°

Loss on Drying 〈731〉

Analysis: Dry under vacuum at 105° for 1 h.

Acceptance criteria: NMT 0.5%

Clarity of Solution

Sample solution: 1 mg/mL of Equilin prepared as follows. Add 100 mg to 100 mL of 1 N sodium hydroxide in a 125 mL conical flask.

Analysis: Heat the Sample solution on a steam bath until solution is complete, then cool, and transfer to a 100-mL color-comparison tube.

Acceptance criteria: The solution is clear.

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight, light-resistant containers.

USP Reference Standards 〈11〉

USP Equilin RS