Application of 1H-NMR spectroscopy to validation of berberine alkaloid reagents and to chemical evaluation of Coptidis Rhizoma

Berberine, palmatine, and coptisine are major pharmacologically active protoberberine alkaloids in Coptidis Rhizoma, and have been used as indices for chemical evaluation of the crude drug. H-1-NMR spectroscopy was applied to determination of purities of commercial reagents of protoberberine alkaloids. The purities of the alkaloids were calculated from the ratios of the intensities of the H-13 singlet signal at about delta 8.7 ppm of target protoberberine alkaloids to integration of a hexamethyldisilane (HMD) signal at 0 ppm. The concentration of HMD was corrected with SI traceability using potassium hydrogen phthalate of certified reference material (CRM) grade. The purity of the reagent estimated by the H-1-NMR was, in general, lower than that claimed by the manufacturer, leading to over-estimation of the alkaloid contents of Coptidis Rhizoma when determined by HPLC. The present quantitative H-1-NMR method was also applicable to direct determination of protoberberine alkaloid contents in Coptidis Rhizoma.