Potassium Benzoate

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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C₇H₅KO₂ 160.21

Benzoic acid, potassium salt;

Potassium benzoate CAS RN^®: 582-25-2.

1 DEFINITION

Potassium Benzoate contains NLT 99.0% and NMT 101.0% of potassium benzoate (C₇H₅KO₂), calculated on the anhydrous basis.

2 IDENTIFICATION

Change to read:

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

Sample: Undried sample

Acceptance criteria: Meets the requirements

B. Potassium Benzoate imparts a violet color to a nonluminous flame. Because the presence of small quantities of sodium masks the color, screen out the yellow color produced by sodium by viewing through a blue filter that blocks emission at 589 nm (sodium) but is transparent to emission at 404 nm (potassium). [Note—Traditionally, cobalt glass has been used, but other suitable filters are commercially available.]

C. The retention time of the major peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay.

3 ASSAY

3.1 Procedure

Solution A: Adjust a 20 mM solution of monobasic potassium phosphate with phosphoric acid to a pH of 2.5.

Mobile phase: Solution A and acetonitrile (70:30)

Diluent: Water and acetonitrile (50:50)

System suitability solution: 0.1 mg/mL of USP Salicylic Acid RS and 0.1 mg/mL of USP Benzoic Acid RS in Diluent

Standard solution: 0.1 mg/mL of USP Benzoic Acid RS in Diluent

Sample solution: 0.1 mg/mL of Potassium Benzoate in Diluent

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 230 nm

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

Column temperature: 25°

Flow rate: 1.0 mL/min

Injection volume: 10 µL

System suitability

Samples: System suitability solution and Standard solution

[Note—The relative retention times for benzoic acid and salicylic acid are approximately 1 and 1.2, respectively.]

Suitability requirements

Resolution: NLT 3.0 between benzoic acid and salicylic acid, System suitability solution

Tailing factor: NMT 2.0 for benzoic acid, Standard solution

Relative standard deviation: NMT 0.5% for benzoic acid, Standard solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of potassium benzoate (C₇H₅KO₂) in the portion of Potassium Benzoate taken:

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

r_U = peak area of benzoic acid from the Sample solution

r_S = peak area of benzoic acid from the Standard solution

C_S = concentration of USP Benzoic Acid RS in the Standard solution, corrected for purity (mg/mL)

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

M_r₁ = molecular weight of potassium benzoate, 160.21

M_r₂ = molecular weight of benzoic acid, 122.12

Acceptance criteria: 99.0%–101.0% on the anhydrous basis

4 SPECIFIC TESTS

Alkalinity

Sample: 2 g

Analysis: Dissolve the Sample in 20 mL of hot water, and add 2 drops of phenolphthalein TS.

Acceptance criteria: If a pink color is produced, it is discharged by the addition of 0.20 mL of 0.10 N sulfuric acid.

Water Determination 〈921〉, Method I: NMT 1.5%

5 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers.

USP Reference Standards 〈11〉

USP Benzoic Acid RS

USP Potassium Benzoate RS

USP Salicylic Acid RS