Thiabendazole

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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C₁₀H₇N₃S 201.25

1H-Benzimidazole, 2-(4-thiazolyl)-;

2-(4-Thiazolyl)benzimidazole CAS RN®: 148-79-8; UNII: N1Q45E87DT.

Change to read:

1 DEFINITION

Thiabendazole contains NLT 98.0% and NMT 101.0% of thiabendazole (C₁₀H₇N₃S), calculated on the dried basis.

[Note—Thiabendazole labeled solely for veterinary use is exempt from the requirements of the tests for Residue on Ignition 〈281〉

(USP 1-Aug- 2022) and Organic Impurities.]

2 IDENTIFICATION

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A. Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197K. Do not dry the Standard nor the Sample. (USP 1-Aug-2022)

Change to read:

B. Spectroscopic Identification Tests 〈197〉, Ultraviolet-Visible Spectroscopy: 197U

Standard solution: 5 μg/mL of USP Thiabendazole RS in 0.1 N hydrochloric acid (USP 1-Aug-2022)

Sample solution: 5 μg/mL in 0.1 N hydrochloric acid

Acceptance criteria: Meets the requirements

C.

Solution A: Dissolve 20 g of ferric ammonium sulfate in 75 mL of water, add 10 mL of 1 N sulfuric acid, and dilute with water to 100 mL.

Sample: 5 mg of Thiabendazole

Analysis: Dissolve the Sample in 5 mL of 0.1 N hydrochloric acid, add 3 mg of p-phenylenediamine dihydrochloride, and shake to dissolve.

Add 0.1 g of zinc dust, mix, and allow to stand for 2 min. Add 5 mL of Solution A.

Acceptance criteria: A blue or blue-violet color develops.

D. The R value of the principal spot of the Identi

cation solution corresponds to that of Standard solution A, as obtained in the test for Organic Impurities.

3 ASSAY

Procedure

Sample: 160 mg of Thiabendazole

Analysis: Dissolve the Sample in 10 mL of glacial acetic acid. Add 50 mL of acetic anhydride, 1 mL of mercuric acetate TS, and 2 drops of crystal violet TS. Titrate with 0.1 N perchloric acid VS (the color change at the endpoint is from blue to blue-green). Perform a blank determination, and make any necessary correction. Each milliliter of 0.1 N perchloric acid is equivalent to 20.13 mg of thiabendazole (C₁₀H₇N₃S).

Acceptance criteria: 98.0%–101.0% on the dried basis

4 IMPURITIES

Residue on Ignition 〈281〉: NMT 0.1%

Delete the following:

Selenium 〈291〉

Sample: 200 mg of Thiabendazole

Acceptance criteria: NMT 0.003% (USP 1-Aug-2022)

Organic Impurities

Standard stock solution: 1.0 mg/mL of USP Thiabendazole RS in glacial acetic acid

Standard solutions: Dilute Standard stock solution as per Table 1 with glacial acetic acid to obtain Standard solutions A, B, and C having the following compositions:

Table 1

Sample solution: 50 mg/mL of Thiabendazole in glacial acetic acid

Identification solution: 0.25 mg/mL of Thiabendazole in glacial acetic acid, from Sample solution

Chromatographic system

(See Chromatography 〈621〉, General Procedures, Thin-Layer Chromatography.)

Mode: TLC

Adsorbent: 0.25-mm layer of chromatographic silica gel mixture

Application volume: 10 μL

Developing solvent system: Toluene, glacial acetic acid, acetone, and water (60:20:8:2)

Analysis

Samples: Standard solutions, Sample solution, and Identification solution Develop in the Developing solvent system until the solvent front has moved three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and allow the solvent to evaporate. Examine the plate under short-wavelength UV light, and compare the intensities of any secondary spots observed in the chromatogram of the Sample solution with those of the principal spots in the chromatograms of the Standard solutions.

Acceptance criteria: No secondary spot from the chromatogram of the Sample solution is larger or more intense than the principal spot of the Standard solution (NMT 0.5%), and the sum of the intensities of all secondary spots of the Sample solution corresponds to NMT 1.0%.

5 SPECIFIC TESTS

Melting Range or Temperature 〈741〉: 296°–303°

Loss on Drying 〈731〉

Sample: Dry in vacuum at 100° for 2 h.

Acceptance criteria: NMT 0.5%

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers.

USP Reference Standards 〈11〉

USP Thiabendazole RS