Ethinyl Estradiol

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

Ethinyl Estradiol contains NLT 97.0% and NMT 102.0% of C₂₀H₂₄O₂, 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

Wavelength: 281 nm

Acceptance criteria: Absorptivities, calculated on the dried basis, do not differ by more than 3.0%.

3 ASSAY

Procedure

Mobile phase: Acetonitrile and water (1:1)

Internal standard solution: 0.5 mg/mL of ethylparaben in Mobile phase

Standard solution: 0.2 mg/mL of USP Ethinyl Estradiol RS in Mobile phase, prepared as follows. Transfer 10 mg of USP Ethinyl Estradiol RS to a 50-mL volumetric flask, and add 10 mL of Mobile phase and 5.0 mL of Internal standard solution. Dilute with Mobile phase to volume.

Sample stock solution: 1.0 mg/mL of Ethinyl Estradiol in Mobile phase

Sample solution: 0.2 mg/mL of Ethinyl Estradiol, prepared as follows. Combine 10.0 mL of the Sample stock solution and 5.0 mL of Internal standard solution in a 50-mL volumetric flask. Dilute with Mobile phase to volume.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 280 nm

Column: 4.6-mm × 15-cm; packing L1

Flow rate: 1 mL/min

Injection size: 25 μL

System suitability

Sample: Standard solution

[Note—The relative retention times for ethylparaben and ethinyl estradiol are about 0.6 and 1.0, respectively.]

Suitability requirements

Resolution: NLT 4.5 between the ethylparaben and ethinyl estradiol peaks

Relative standard deviation: NMT 2.0%

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of ethinyl estradiol (C₂₀H₂₄O₂) taken:

Result = (R_U/R_S) × (C_S/C_U) × 100

R_U = peak response ratio from the Sample solution

R_S = peak response ratio from the Standard solution

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

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

Acceptance criteria: 97.0%–102.0% on the dried basis

4 IMPURITIES

Completeness of Solution: Dissolve 100 mg in 5 mL of alcohol; the solution is clear and free from undissolved solid.

5 SPECIFIC TESTS

Melting Range or Temperature 〈741〉: 180°–186°. It may exist also in a polymorphic modification, melting at 142°–146°.

Optical Rotation, Specific Rotation〈781S〉

Sample solution: 50 mg/mL, using sonication if necessary, in colorless pyridine from a freshly opened container

Acceptance criteria: −28.0° to −29.5°

Loss on Drying 〈731〉: Dry a sample at 105° for 3 h: it loses NMT 1.0% of its weight.

6 ADDITIONAL REQUIREMENTS

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

USP Reference Standards 〈11〉

USP Ethinyl Estradiol RS