Hydralazine 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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C₈H₈N₄ · HCl 196.64

Phthalazine, 1-hydrazino-, monohydrochloride;

1-Hydrazinophthalazine monohydrochloride CAS RN®: 304-20-1; UNII: FD171B778Y.

1 DEFINITION

Hydralazine Hydrochloride contains NLT 98.0% and NMT 102.0% of hydralazine hydrochloride (C₈H₈N₄ · HCl), calculated on the dried basis.

2 IDENTIFICATION

Change to read:

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

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

C. Identification Tests—General 〈191〉, Chemical Identification Tests, Chloride

Sample solution: 0.25 mg/mL of Hydralazine Hydrochloride in water

Acceptance criteria: Meets the requirements

3 ASSAY

Procedure

Mobile phase: Dissolve 1.44 g of sodium dodecyl sulfate and 0.75 g of tetrabutylammonium bromide in 770 mL of water, and add 230 mL of acetonitrile. Adjust with 0.1 N sulfuric acid to a pH of 3.0.

Diluent: 0.1 N acetic acid

System suitability stock solution: 0.25 mg/mL of USP Hydralazine Hydrochloride RS and 0.05 mg/mL of USP Phthalazine RS in Diluent System suitability solution: 25 µg/mL of USP Hydralazine Hydrochloride RS and 5 µg/mL of USP Phthalazine RS in Diluent from the System suitability stock solution

Standard stock solution: 0.4 mg/mL of USP Hydralazine Hydrochloride RS in Diluent

Standard solution: 40 µg/mL of USP Hydralazine Hydrochloride RS in Diluent from the Standard stock solution Sample stock solution: 0.4 mg/mL of Hydralazine Hydrochloride in Diluent

Sample solution: 40 µg/mL of Hydralazine Hydrochloride in Diluent prepared as follows. Transfer a suitable amount of the Sample stock solution to a suitable volumetric flask. Dilute with Diluent to volume and filter, discarding the first 10 mL of the filtrate.

3.1 Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 230 nm

Column: 4.0-mm × 25-cm; 10-µm packing L10

Flow rate: 1 mL/min

Injection volume: 25 µL

3.2 System suitability

Samples: System suitability solution and Standard solution

[Note—The relative retention times for phthalazine and hydralazine hydrochloride are 0.65 and 1.0, respectively.] Suitability requirements

Resolution: NLT 4.0 between the phthalazine and hydralazine peaks, System suitability solution

Relative standard deviation: NMT 0.73%, Standard solution

3.3 Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of hydralazine hydrochloride (C₈H₈N₄ · HCl) in the portion of Hydralazine Hydrochloride taken: 

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

r_U = peak response of hydralazine from the Sample solution

r_S = peak response of hydralazine from the Standard solution

C_S = concentration of USP Hydralazine Hydrochloride RS in the Standard solution (µg/mL)

C_U = concentration of Hydralazine Hydrochloride in the Sample solution (µg/mL)

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

4 IMPURITIES

Residue on Ignition 〈281〉: NMT 0.1%

4.1 Organic Impurities

Mobile phase, Diluent, and System suitability solution: Prepare as directed in the Assay.

Standard solution: 0.001 mg/mL of USP Hydralazine Hydrochloride RS in Diluent. Sonication may be necessary for complete dissolution. Sample solution: 0.5 mg/mL of Hydralazine Hydrochloride in Diluent prepared as follows. Transfer a suitable amount of Hydralazine Hydrochloride to a suitable volumetric ask. Add Diluent to ll about 60% of the total volume, and sonicate to dissolve. Cool, and dilute with Diluent to volume.

4.1.1 Chromatographic system

Proceed as directed in the Assay, except for Injection volume.

Injection volume: 20 µL

4.1.2 System suitability

Samples: System suitability solution and Standard solution

Suitability requirements

Resolution: NLT 4.0 between the phthalazine and hydralazine peaks, System suitability solution

Relative standard deviation: NMT 5.0%, Standard solution

4.1.3 Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of each impurity in the portion of Hydralazine Hydrochloride taken:

Result = (r_U /r_S )× (C_S /C_U)) × (1/F) × 100

r_U = peak response of each impurity from the Sample solution

r_S = peak response of hydralazine from the Standard solution

C_S = concentration of USP Hydralazine Hydrochloride RS in the Standard solution (mg/mL)

C_U = concentration of Hydralazine Hydrochloride in the Sample solution (mg/mL)

F = relative response factor (see Table 1)

Acceptance criteria: See Table 1.

Table 1

^a Total impurities include specified and unspecified impurities.

5 Limit of Hydrazine

Buffer: Dissolve 5.82 g of dibasic sodium phosphate and 3.81 g of monobasic potassium phosphate in 1 L of water, and adjust with either 1 N sodium hydroxide or 1 N phosphoric acid to a pH of 7.0 ± 0.1.

Mobile phase: Dissolve 300 mg of edetate disodium in 300 mL of water in a 1-L volumetric ask. Dilute with acetonitrile to volume. Benzaldehyde solution: Transfer 1.0 mL of benzaldehyde to a 100-mL volumetric ask, and dilute with a mixture of methanol and water (9:1) to volume.

Acetonitrile solution: Transfer 300 mL of water to a 1000-mL volumetric ask, and dilute with acetonitrile to volume.

Standard stock solution: 0.65 mg/mL of hydrazine dihydrochloride in water 

Standard solution 1: 0.325 µg/mL of hydrazine dihydrochloride in water from Standard stock solution 

Standard solution 2: Transfer 1.0 mL of Standard solution 1 to a 10-mL ask. Add 4.0 mL of Benzaldehyde solution, and shake by mechanical means for 20 min. 

Standard solution 3: Transfer 2.0 mL of Standard solution 2 to a 5-mL volumetric ask, and dilute with Acetonitrile solution to volume. Extraction column: Use a freshly conditioned solid phase extraction column containing benzenesulfonic acid strong cation-exchange packing with a sorbent-mass to column volume ratio of 500 mg/3 mL, or equivalent. The column is conditioned as follows. Wash the column with two 2.0-mL portions of hexanes, and dry under vacuum for 2 min. Wash the column with two 2.0-mL portions of methanol, two 2.0-mL portions of water, and two 2.0-mL portions of Buffer. At no time after the hexanes wash should the column be allowed to dry out. Sample solution: Transfer about 20 mg of Hydralazine Hydrochloride to a 10-mL reaction vessel, and dissolve in 1.0 mL of water. Add 4.0 mL of Benzaldehyde solution, and shake by mechanical means for 20 min. Pipet 2.0 mL of this solution into the Extraction column and elute into a 5-mL volumetric ask. Wash the Extraction column with two 1.5-mL portions of the Acetonitrile solution, collecting the washings with the eluate, and dilute with Acetonitrile solution to volume. 

5.1 Chromatographic system 

(See Chromatography 〈621〉, System Suitability.) 

Mode: LC 

Detector: UV 310 nm 

Column: 4.0-mm × 25-cm; 10-µm packing L1 

Flow rate: 1 mL/min 

Injection volume: 20 µL 

5.2 System suitability 

Sample: Standard solution 3 

[Note—The relative retention times for hydralazine and hydrazine are about 1.0 and 1.5, respectively.] 

Suitability requirements 

Relative standard deviation: NMT 2.0% 

5.3 Analysis 

Samples: Standard solution 3 and Sample solution 

Calculate the percentage of hydrazine in the portion of hydralazine hydrochloride (C₈H₈N₄ · HCl) taken: 

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

r_U = peak response of hydrazine from the Sample solution 

r_S = peak response of hydrazine from Standard solution 3

C_S = concentration of hydrazine dihydrochloride in Standard solution 3 (µg/mL) 

C_U = concentration of Hydralazine Hydrochloride in the Sample solution (µg/mL) 

M_r1 = molecular weight of hydrazine, 32.05

M_r2 = molecular weight of hydrazine dihydrochloride, 104.97

Acceptance criteria: NMT 0.001%

6 SPECIFIC TESTS

pH 〈791〉

Sample solution: 20 mg/mL of Hydralazine Hydrochloride in water

Acceptance criteria: 3.5–4.2

Loss on Drying 〈731〉

Analysis: Dry at 110° for 15 h.

Acceptance criteria: NMT 0.5%

7 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers. Store at controlled room temperature.

USP Reference Standards 〈11〉

USP Hydralazine Hydrochloride RS

USP Phthalazine RS     C₈H₆N₂             130.15