Evaluation of the Folin-Ciocalteu Method and Quantification of Total Tannins in Stem Barks and Pods from Libidibia ferrea (Mart. ex Tul) L. P. Queiroz

The stem bark and pods of juca are widely used in Brazilian folk medicine and, despite their therapeutic relevancies, there are insufficient reports about their quality control. Both herbal drugs from the species are rich in tannins, which showed a lot of biological and economic interest. Thus, the purpose of this study was to evaluate the method for quantification of tannins in the stem bark and pods from L. ferrea. The performance of the method was tested against the influence of the most relevant parameters (reaction time; amount of drug; type and amount of precipitationagents; and, concentration of the reagents). The procedure was validated according to the literature. After optimization, the experimental conditions were established as: 30 min of reaction; lambda of 760 nm; 1.0 mL of Folin-Ciocalteu; 29% of Na2CO3 (w/v); and, skin powder as complexion agent. The method validation showed that the instrumental response was linear and sensitive to the investigated analyte. The method presented the necessary precision (RSD < 2.19%) and accuracy (96.84%409.13%), as recommended by the official codex. Moreover, the deliberate introduction of experimental variations showed the stability of the procedure error against external sources (RSD < 2.42%). In conclusion, the data demonstrated the suitability of the method and can be used as anappropriate analytical tool for quality control of herbal drugs from L. ferrea.