Sorbic Acid

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

Change to read:

Sorbic Acid contains NLT 98.0% (NF 1-Dec-2019) and NMT 102.0% (NF 1-Dec-2019) of sorbic acid (C₆H₈O₂), calculated on the anhydrous basis.

2 IDENTIFICATION

Change to read:

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

B. A 1-in-400,000 solution in isopropyl alcohol exhibits an absorbance maximum at 254 ± 2 nm.

3 ASSAY

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Procedure

Solution A: 0.1% (v/v) trifluoroacetic acid in water

Solution B: 0.1% (v/v) trifluoroacetic acid in methanol

Mobile phase: See Table 1.

Table 1

Diluent: Water and methanol (1:1, v/v)

System suitability solution: Prepare 0.1 mg/mL of USP Sorbic Acid RS in Diluent first and then treat the solution with UV irradiation to generate ~1% degradation of sorbic acid (based on area%).1

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

Sample solution: 0.1 mg/mL of Sorbic Acid in Diluent

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 264 nm

Column: 4.6-mm × 15-cm; 3.5-μm packing L1

Column temperature: 40°

Flow rate: 1.0 mL/min

Injection volume: 10 μL

Run time: 30 min

System suitability

Samples: System suitability solution and Standard solution

[Note—The approximate relative retention times of related substances are listed in Table 2.]

Suitability requirements

Resolution: NLT 1.5 between sorbic acid and sorbic acid trans, cis isomer, System suitability solution

Tailing factor: NMT 2.0, determined from sorbic acid, Standard solution

Relative standard deviation: NMT 2.0%, determined from sorbic acid, Standard solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of sorbic acid in the sample taken:

Result = (r_U/r_S) × (C_S/C_U) × 100

r_U = peak area of sorbic acid from the Sample solution

r_S = peak area of sorbic acid from the Standard solution

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

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

Acceptance criteria: 98.0%–102.0% on the anhydrous basis

Table 2

^a (Z,Z)-Sorbic acid.

^b (Z,E)-Sorbic acid.

^c (E,Z)-Sorbic acid.

[Note—Sorbic acid cis, trans isomer and sorbic acid trans, cis isomer might co-elute in some columns, which has no effect on assay analysis.] (NF 1-Dec-2019)

4 IMPURITIES

Add the following:

Limit of Aldehyde

Decolorized fuchsin solution: Dissolve 0.1 g of basic fuchsin in 60 mL of water. Add a solution containing 1 g of anhydrous sodium sulfite in 10 mL of water. Slowly and with continuous shaking add 2 mL of hydrochloric acid. Dilute with water to 100 mL. Allow to stand protected from light for at least 12 h, decolorize with activated charcoal and filter. If the solution becomes cloudy, filter before use. If on standing the solution becomes violet, decolorize again by adding activated charcoal.

Test for sensitivity: To 1.0 mL of the Decolorized fuchsin solution add 1.0 mL of water and 1.0 mL of alcohol, aldehyde-free. Add 0.2 mL of a solution containing 0.1 g/L of formaldehyde (CH₂O). A pale-pink color develops within 5 min.

Storage of Decolorized fuchsin solution: Protected from light

Acetaldehyde standard solution: 100 μg/mL of acetaldehyde (C₂H₄O). Dissolve 1.0 g of acetaldehyde in 2-propanol and dilute with the same solvent to 100.0 mL. Dilute 5.0 mL of the solution with 2-propanol to 500.0 mL. Prepare immediately before use.

Standard solution: Add 1 mL of Decolorized fuchsin solution to a mixture of 1.5 mL of Acetaldehyde standard solution, 4 mL of 2-propanol, and 4.5 mL of water.

Sample solution: Dissolve 1.0 g of the sample in a mixture of 30 mL of water and 50 mL of 2-propanol, adjust with 0.1 N hydrochloric acid or 0.1 N sodium hydroxide to a pH of 4 and dilute with water to 100 mL.

Analysis: To 10 mL of the Sample solution add 1 mL of Decolorized fuchsin solution and allow to stand for 30 min. Any color in the solution is not more intense than that in the Standard solution prepared at the same time.

Acceptance criteria: NMT 0.15%, as acetaldehyde (C₂H₄O) (NF 1-Dec-2019)

Residue on Ignition 〈281〉: NMT 0.2%

5 SPECIFIC TESTS

Melting Range or Temperature 〈741〉: 132°–135°

Water Determination 〈921〉, Method I: NMT 0.5%

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers, protected from light, and avoid exposure to excessive heat.

USP Reference Standards 〈11〉

USP Sorbic Acid RS