Tolazoline Hydrochloride
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C10H12N2·HCl 196.68

1H-Imidazole, 4,5-dihydro-2-(phenylmethyl)-, monohydrochloride.
2-Benzyl-2-imidazoline monohydrochloride [59-97-2].
» Tolazoline Hydrochloride contains not less than 98.0 percent and not more than 101.0 percent of C10H12N2·HCl, calculated on the dried basis.
Packaging and storage— Preserve in well-closed containers. Store at 25, excursions permitted between 15 and 30.
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%.
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:
Dilution Concentration
(µg RS per mL)
(%, for
with test specimen)
A undiluted 100 0.5
B 4 in 5 80 0.4
C 3 in 5 60 0.3
D 2 in 5 40 0.2
E 1 in 5 20 0.1
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%.
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.
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Sujatha Ramakrishna, Ph.D.
(MDCV05) Monograph Development-Cardiovascular
Reference Standards Lili Wang, Technical Services Scientist
USP32–NF27 Page 3765
Pharmacopeial Forum: Volume No. 29(5) Page 1588