RESUMO
INTRODUCTION: The usual quality control for Uncaria tomentosa (Willd. ex Schult.) DC. barks requires highly specific analytical standards and methods based on high-performance liquid chromatography (HPLC), which impacts the costs of the analytical process and the final products. OBJECTIVE: To obtain an analytical reference standard of mitraphylline by isolation from U. tomentosa barks and develop a spectrophotometric method for determination of total alkaloids in samples of U. tomentosa. METHODOLOGY: An alkaloid-enriched extract was obtained by acid-base partition and mitraphylline was selectively precipitated using an 80:20 v/v toluene/hexane solution. The compound was characterised by HPLC-UV/DAD (diode-array detector), mass spectrometry, UV-visible, infrared (IR) and 1 H- and 13 C-nuclear magnetic resonance (NMR) spectroscopy. Sample preparation for the spectrophotometric method consisted of an extraction with boiling methanol (3 × 10 mL, 15 min), followed by a strong cation exchange solid phase extraction (SCX-SPE) clean-up. RESULTS: Mitraphylline with a purity of 98% was isolated in 0.05% m/m yield. All characterisation results were in agreement with previous published data. The spectrophotometric method showed linear range between 0.40 and 20 µg/mL; limits of detection and quantification of 0.15 and 0.49 µg/mg, respectively; dispersion of results lower than 5% for repeatability and intermediate precision; statistically proven accuracy by comparison with reference values obtained by Soxhlet and an HPLC-UV/DAD method; and robustness in relation to sample mass extracted and extraction time. CONCLUSION: The methods developed to obtain mitraphylline analytical standard from U. tomentosa barks and to determine total alkaloids by spectrophotometry provided a cheaper and faster quality control alternative for U. tomentosa samples.
