Colorimetric and spectrophotometric determinations of hydrastis alkaloids in pharmaceutical preparations

Hydrastine, canadine, and berberine were determined by the acid-dye technique. At pH 5.6, both the tertiary and the quaternary hydrastis alkaloids formed ion-pairs with bromcresol purple. The liberated hydrastine and canadine from the alkaloid-dye complexes were determined spectrophotometrically in the presence of berberine by the three-wavelength method of analysis. However, berberine could not be assayed successfully by this method due to significant partitioning in the aqueous phase during extraction. At pH 7.2, only berberine could ion-pair with bromcresol purple to form a chloroform-extractable complex. Consequently, the berberine content was analyzed selectively through the colorimetric determination of the combined dye at 580 nm. The suitability of the proposed methods was examined through the analyses of synthetic mixtures of hydrastis alkaloids and samples of hydrastis tincture and liquid extract. Percentage recoveries were 98.2-101.4 for the synthetic mixtures and 98.4-101.7 for the tincture and liquid extract spiked with berberine.