Propylparaben Sodium

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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C₁₀H₁₂NaO₃ 202.20

Benzoic acid, 4-hydroxy-, propyl ester, sodium salt;

Propyl p-hydroxybenzoate, sodium salt;

Sodium 4-propoxycarbonylphenolate CAS RN®: 35285-69-9.

1 DEFINITION

Propylparaben Sodium contains NLT 94.0% and NMT 102.0% of propylparaben sodium (C₁₀H₁₂NaO₃), calculated on the anhydrous basis.

2 IDENTIFICATION

A. Standard: 0.5 g of USP Propylparaben RS

Sample: 0.5 g

Analysis: Dissolve the Sample in 5 mL of water. Acidify with hydrochloric acid, and filter the resulting precipitate. Wash the precipitate with water, and dry over silica gel for 5 h. Repeat with the Standard.

Acceptance criteria: The IR absorption spectrum of a Mineral oil dispersion of the Sample exhibits maxima only at the same wavelengths as those of a mineral oil dispersion of the Standard.

B. Sample solution: Ignite 0.3 g of Propylparaben Sodium, cool, and dissolve the residue in 3 mL of 3 N hydrochloric acid.

Acceptance criteria: A platinum wire dipped in the Sample solution imparts an intense, persistent yellow color to a nonluminous flame.

3 ASSAY

3.1 Procedure

Mobile phase: Methanol and a 6.8-g/L solution of potassium dihydrogen phosphate (65:35, v/v)

System suitability solution: 5.0 μg/mL each of p-hydroxybenzoic acid, USP Ethylparaben RS, and USP Propylparaben RS in Mobile phase

Standard solution: Dissolve 50.0 mg of USP Propylparaben RS in 2.5 mL of methanol, and dilute with Mobile phase to 50.0 mL. Dilute 10.0 mL of this solution with Mobile phase to 100.0 mL.

Sample solution: Dissolve 50.0 mg of Propylparaben Sodium in 2.5 mL of methanol, and dilute with Mobile phase to 50.0 mL. Dilute 10.0 mL of this solution with Mobile phase to 100.0 mL.

3.2 Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 272 nm

Column: 4.6-mm × 15-cm; 5-μm packing L1

Flow rate: 1.3 mL/min

Injection volume: 10 μL

Run time: About 2.5 times the retention time of the propylparaben peak

3.3 System suitability

Samples: System suitability solution and Standard solution

[Note—The retention time of propylparaben is about 4.0 min; the relative retention times for p-hydroxybenzoic acid, ethylparaben, and propylparaben are about 0.4, 0.7, and 1.0, respectively.]

3.4 Suitability requirements

Resolution: NLT 3.0 between the ethylparaben and propylparaben peaks, System suitability solution

Relative standard deviation: NMT 0.85% for six injections, Standard solution

3.5 Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of propylparaben sodium (C₁₀H₁₂NaO₃) in the portion of Propylparaben Sodium taken:

Result = P × (r_U × C_S )/(r_S × C_U ) × (M /M )

P = labeled purity of USP Propylparaben RS expressed as a percentage

r_U = peak area of propylparaben from the Sample solution

C_S = concentration of propylparaben in the Standard solution

r_S = peak area of propylparaben from the Standard solution

C_U = concentration of Propylparaben Sodium in the Sample solution

M = molecular weight of propylparaben sodium, 202.20

M = molecular weight of propylparaben, 180.20

Acceptance criteria: 94.0%–102.0% on the anhydrous basis

4 IMPURITIES

Related Compounds

Mobile phase, System suitability solution, Sample solution, and Chromatographic system: Proceed as directed in the Assay.

Standard solution: Dilute 1.0 mL of the Sample solution with Mobile phase to 20.0 mL. Dilute 1.0 mL of this solution with Mobile phase to 10.0 mL.

System suitability

Sample: System suitability solution

[Note—The retention time of propylparaben is about 4.0 min; the relative retention times for p-hydroxybenzoic acid, ethylparaben, and propylparaben are about 0.4, 0.7, and 1.0, respectively.]

Suitability requirements

Resolution: NLT 3.0 between the ethylparaben and propylparaben peaks

Analysis

Samples: Standard solution and Sample solution Acceptance criteria p-Hydroxybenzoic acid: NMT 4.0%; the peak area in the Sample solution, multiplied by 1.4 to correct for the calculation of content, is NMT 8 times the area of the principal peak in the Standard solution.

Unspecified impurities: NMT 0.5%; the peak area of each impurity in the Sample solution is NMT the area of the principal peak in the Standard solution.

Total impurities: NMT 1.0%; the total peak area for all unspecified impurities in the Sample solution is NMT twice the area of the principal peak in the Standard solution.

Chloride and Sulfate, Chloride 〈221〉

Standard solution: 0.10 mL of 0.020 N hydrochloric acid

Sample: 0.2 g

Analysis: Proceed as directed in the chapter.

Acceptance criteria: 0.035%; the Sample shows no more chloride than the Standard solution.

Chloride and Sulfate, Sulfate 〈221〉

Standard solution: 0.30 mL of 0.020 N sulfuric acid

Sample: 0.25 g

Analysis: Proceed as directed in the chapter.

Acceptance criteria: 0.12%; the Sample shows no more sulfate than the Standard solution.

5 SPECIFIC TESTS

pH 〈791〉

Sample solution: 1 mg/mL

Acceptance criteria: 9.5–10.5

Water Determination, Method I 〈921〉: NMT 5.0%

Completeness of Solution 〈641〉

Sample solution: Dissolve 1 g in water.

Acceptance criteria: Meets the requirements

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers.

USP Reference Standards 〈11〉

USP Ethylparaben RS

USP Propylparaben RS