Abstract
Stability tests are essential to assuring herbal derivative quality, especially because of the complexity of the herbal matrix. To monitor the stability of Sambucus nigra L. flower tincture, a practical liquid chromatography (LC)-UV method was developed and validated. Rutin, the flower's pharmacopeial marker, in addition to other markers, isoquercitrin and quercetin, were quantified. The last two represent the degradation products of glycosylated flavonoids. In addition, other chromatographic peaks exhibiting typical flavonoid UV absorption profiles (total flavonoids) were also quantified and expressed in rutin equivalents. The method was developed with a reverse phase C18 column, using a gradient mobile phase at 0.7 mL min -1 at 30°C. The herbal drug and tincture obtained by percolation at 60 °C with ethanol 25% (v/v) were submitted to accelerated (40°C/75% RH, 2 months) and long duration (15–30°C, 6 months) studies. The LC-UV method was linear in the ranges of 1–200 μg mL-1 (rutin) and 1–100 μg mL-1 (isoquercitrin and quercetin), without interference of herbal matrix, and was precise (RSD ≤ 2.0% for intra and interday precision), selective, and robust (changes in mobile phase flow, pH and temperature). The tincture revealed the presence of quercetin, which was absent in the herbal drug, likely due to the hydrolysis process. After 2 months under accelerated study, the total flavonoids in the tincture decreased by approximately 20%, and after 6 months at room temperature, they decreased by approximately 30%. These results indicate the thermolability of the S. nigra tincture and the importance of monitoring phytomedicine stability.