Tolazoline Hydrochloride

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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C₁₀H₁₂N₂ · HCl 196.68

1H-Imidazole, 4,5-dihydro-2-(phenylmethyl)-, monohydrochloride.

2-Benzyl-2-imidazoline monohydrochloride CAS RN®: 59-97-2; UNII: E669Z6S1JG.

Tolazoline Hydrochloride contains not less than 98.0 percent and not more than 101.0 percent of C₁₀H₁₂N₂ · HCl, calculated on the dried basis.

1 Packaging and storage

Preserve in well-closed containers. Store at 25°, excursions permitted between 15° and 30°.

1.1 USP Reference standards 〈11〉

USP Tolazoline Hydrochloride RS

2 Identification

Change to read:

A: Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197M.

B: The Rf value of the principal spot in the chromatogram of the Identification corresponds to that of Standard solution A, as obtained in the test for Chromatographic purity.

Melting range 〈741〉: between 172.0° and 176.0°.

Loss on drying 〈731〉—Dry it in vacuum over silica gel for 4 hours: it loses not more than 0.2% of its weight.

Residue on ignition 〈281〉: not more than 0.1%.

3 Chromatographic purity

Standard solutions-Dissolve USP Tolazoline Hydrochloride RS in methanol, and mix to obtain Standard solution A having a known concentration of 100 µg per mL. Quantitatively dilute with methanol to obtain Standard solutions, designated below by letter, having the following compositions:

Test solution-Dissolve an accurately weighed quantity of Tolazoline Hydrochloride in methanol to obtain a solution containing 20 mg per mL.

Identification solution-Quantitatively dilute a portion of the Test solution with methanol to obtain a solution containing 100 µg per mL.

Detection reagent-Prepare (1) a solution of 0.5 g of potassium iodide in 50 mL of water, and (2) a solution of 1.5 g of soluble starch in 50 mL of boiling water. Just prior to use, mix 10 mL of each solution with 3 mL of alcohol.

Procedure-Apply separately 5 µL of the Test solution, 5 µL of the Identification solution, and 5 µL of each Standard solution to a suitable thin-layer chromatographic plate (see Chromatography 〈621〉) coated with a 0.25-mm layer of chromatographic silica gel. Position the plate in a chromatographic chamber, and develop the chromatograms in a solvent system consisting of a mixture of methanol and ammonium hydroxide (95:5) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and allow the plate to dry under a current of warm air for at least 30 minutes. Expose the plate to chlorine gas for not more than 5 minutes, and air-dry until the chlorine has dissipated (about 15 minutes). Spray the plate with Detection reagent, and immediately compare the intensities of any secondary spots observed in the chromatogram of the Test solution with those of the principal spots in the chromatograms of the Standard solutions: the sum of the intensities of all secondary spots obtained from the Test solution corresponds to not more than 1.0%.

4 Assay

Dissolve about 300 mg of Tolazoline Hydrochloride, accurately weighed, in 100 mL of glacial acetic acid; add 25 mL of mercuric acetate TS; and titrate with 0.1 N perchloric acid VS, determining the endpoint potentiometrically (see Titrimetry 〈541〉), using a calomel–glass electrode system. Perform a blank determination, and make any necessary correction. Each mL of 0.1 N perchloric acid is equivalent to 19.67 mg of C₁₀H₁₂N₂ · HCl.