Estriol

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

Estriol contains NLT 97.0% and NMT 102.0% of estriol (C₁₈H₂₄O₃), calculated on the dried basis.

2 IDENTIFICATION

Change to read:

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

Change to read:

B. The retention time of the major peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay. (USP 1-May-2019)

3 ASSAY

Change to read:

Procedure

Solution A: Water

Solution B: Methanol

Mobile phase: See Table 1.

Table 1

Diluent: Methanol and water (1:1)

System suitability solution: 100 μg/mL of USP Estriol RS and 5 μg/mL of USP Estriol Related Compound A RS in Diluent. Sonicate to dissolve as needed.

Standard solution: 100 μg/mL of USP Estriol RS in Diluent. Sonicate to dissolve as needed.

Sample solution: 100 μg/mL of Estriol in Diluent. Sonicate to dissolve as needed.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 220 nm

Column: 4.6-mm × 15-cm; 2.6-μm packing L1

Column temperature: 32°

Flow rate: 1.0 mL/min

Injection volume: 25 μL

System suitability

Samples: System suitability solution and Standard solution

[Note—See Table 2 for the relative retention times.]

Suitability requirements

Resolution: NLT 1.2 between estriol related compound A and estriol, System suitability solution

Tailing factor: NMT 1.5, Standard solution

Relative standard deviation: NMT 0.73%, Standard solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of estriol (C₁₈H₂₄O₃) in the portion of Estriol taken:

Result = (r_U/r_S) × (C_S/C_U) × 100

r_U= peak response from the Sample solution

r_S = peak response from the Standard solution

C_S = concentration of USP Estriol RS in the Standard solution (μg/mL)

C_U = concentration of Estriol in the Sample solution (μg/mL)

(USP 1-May-2019)

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

4 IMPURITIES

Residue on Ignition 〈281〉: NMT 0.1%

Change to read:

Organic Impurities

Solution A, Solution B, Diluent, and Chromatographic system: Proceed as directed in the Assay.

Mobile phase: See Table 2.

Table 2

System suitability stock solution A: 200 μg/mL of USP Estriol RS prepared as follows. Transfer a suitable quantity of USP Estriol RS to an appropriate volumetric flask. Add 50% of the total flask volume of methanol to dissolve, and sonicate to fully dissolve the solids. Dilute with water to volume and mix well.

System suitability stock solution B: 100 μg/mL each of USP Estriol Related Compound A RS, USP Estrone RS, and USP Estradiol RS prepared flas follows. Transfer a suitable quantity of each Reference Standard to an appropriate volumetric flask. Add 80% of the total flask volume of methanol to dissolve, and sonicate to fully dissolve the solids. Dilute with methanol to volume and mix well.

System suitability solution: 100 μg/mL of USP Estriol RS and 5 μg/mL each of USP Estriol Related Compound A RS, USP Estrone RS, and USP Estradiol RS prepared as follows. Transfer 10-mL of System suitability stock solution A into a 20-mL volumetric flask. Add 1 mL of System suitability stock solution B and 1 mL of water. Dilute with Diluent to volume and mix well. Sonicate to dissolve as needed.

Standard solution: 0.4 μg/mL of USP Estriol RS and 2 μg/mL each of USP Estriol Related Compound A RS, USP Estrone RS, and USP Estradiol RS in Diluent. Sonicate to dissolve as needed.

Sample solution: 400 μg/mL of Estriol prepared as follows. Transfer a suitable quantity of Estriol to an appropriate volumetric flask. Add 50% of the total flask volume of methanol to dissolve, and sonicate to fully dissolve the solids. Dilute with water to volume and mix well.

System suitability

Samples: System suitability solution and Standard solution

[Note—See Table 3 for the relative retention times.]

Suitability requirements

Resolution: NLT 1.2 between estriol related compound A and estriol; NLT 1.2 between estrone and estradiol, System suitability solution

Relative standard deviation: NMT 10.0%; estriol, estriol related compound A, estrone, and estradiol, Standard solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of estriol related compound A, estrone, and estradiol in the portion of Estriol taken:

Result = (r_U/r_S) × (C_S/C_U) × 100

r_U = peak response of estriol related compound A, estrone, or estradiol from the Sample solution

r_S = peak response of the corresponding USP Reference Standard from the Standard solution

C_S = concentration of the corresponding USP Reference Standard in the Standard solution (μg/mL)

C_U = concentration of Estriol in the Sample solution (μg/mL)

Calculate the percentage of any individual impurity in the portion of Estriol taken:

Result = (r_U/r_S) × (C_S /C_U) × 100

r_U = peak response of any individual impurity from the Sample solution

r_S= peak response of estriol from the Standard solution

C_S = concentration of USP Estriol RS in the Standard solution (μg/mL)

C_U = concentration of Estriol in the Sample solution (μg/mL)

Acceptance criteria: See Table 3.

Table 3

^a Estra-1,3,5(10)-triene-3,16β,17α-triol.

^b Estra-1,3,5(10)-triene-3,16β,17β-triol.

^c Estra-1,3,5(10)-triene-3,16α,17α-triol.

^d 3-Methoxy-(16α,17β)-estra-1,3,5(10)-triene-16,17-diol.

^e Total impurities exclude estriol related compound A.

(USP 1-May-2019)

5 SPECIFIC TESTS

Optical Rotation 〈781S〉, Procedures, Specific Rotation

Sample solution: 4 mg/mL, in dioxane

Acceptance criteria: +54° to +62°

Loss on Drying 〈731〉

Analysis: Dry at 105° for 3 h.

Acceptance criteria: NMT 0.5% of its weight

Delete the following:

Completeness of Solution

Sample solution: 50 mg/mL in pyridine

Acceptance criteria: The solution is clear and free from undissolved solid. (USP 1-May-2019)

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers.

Change to read:

USP Reference Standards 〈11〉

USP Estradiol RS (USP 1-May-2019)

USP Estriol RS

USP Estriol Related Compound A RS

Estra-1,3,5(10),9(11)-tetraene-3,16α,17β-triol.

C₁₈H₂₂O₃ 286.37

USP Estrone RS

(USP 1-May-2019)