Colorimetric determination of hydralazine with 9-chloroacridine.

A spectrophotometric assay for hydralazine hydrochloride based on the interaction of the drug with 9-chloroacridine has been developed. The interaction shows an absorption maximum at 460 nm and is affected by temperature, heating time, and quantity of acridine reagent used. Color development is maximum when the drug is heated in the presence of a 30-fold molar excess of the acridine in a 50 +/- 1 degree C water bath for 1 hr. The method detects hydralazine hydrochloride in the 10(-5)--10(-6)M range with sensitivity to 0.2 micrograms/mL and 3--4% accuracy. Typical calibration data obtained from linear regression analysis of absorbance at various drug concentrations show r = 0.9997 (n = 6). Hydralazine can be determined in dosage forms that also contain varying quantities of reserpine and hydrochlorothiazide. The 9-chloroacridine method is as sensitive as other spectrophotometric procedures for hydralazine but also more accurate and precise, and involves fewer manipulative steps.